Introduction
Pancreatic cancer is the 12th most commonly diagnosed cancer and the 3rd leading cause of cancer mortality among Canadians and accounts for approximately 2·7% of all newly diagnosed cancer cases and 6·4% of all cancer mortalities in the country. 1,Reference Brenner, Weir and Demers2 In 2020, it was projected that 3,100 men and 2,900 women will be diagnosed with pancreatic cancer and 2,700 men and 2,600 women will die from the disease in Canada. 1,Reference Brenner, Weir and Demers2 Pancreatic ductal adenocarcinoma (PDAC) is the most common form of pancreatic cancer accounting for 85–90% of all pancreatic neoplasms and according to Haeberle et al. Reference Haeberle and Esposito3 and Takayama et al. Reference Takayama, Nakagawa and Sawaki4 about 65–70% of newly diagnosed pancreatic cancer patients will be in the advanced stages (stages III–IV) at initial presentation. Surgical resection currently offers the only potential monomodal cure for PDAC, however, only 10–20% of patients have anatomically resectable cancers at presentation. Reference Takayama, Nakagawa and Sawaki4,Reference Rückert, Pilarsky and Grützmann5 Even among patients with localised tumours and no other contraindications to resection, only about 60% will proceed to surgical resection with curative intent and even then, the majority of patients will eventually succumb to metastatic disease post-operatively. Reference Bergquist, Puig and Shubert6–Reference Takehara, Eguchi and Ohigashi10 Advanced pancreatic cancer has very poor prognosis, with a median survival of 2–6 months for stage IV disease and 6–11 months for stage III disease. The overall 5-year survival among this group of patients is only 5–7% and the majority of patients survive less than 1–2 years. Reference Takayama, Nakagawa and Sawaki4,Reference Takehara, Eguchi and Ohigashi10 Among patients who undergo surgery with curative intent more than 90% develop disease progression within 12–18 months.
Pancreatic cancer has a high mortality rate mainly attributed to being asymptomatic until usually diagnosed at a late stage with advanced disease and according to Deshwar et al., Reference Deshwar, Sugar and Torto11 only 15–20% of patients are diagnosed at a stage that is still operable. The late presentation of pancreatic cancer has the risk of the tumour progressing from being curable (with near-normal life expectancy) to becoming incurable (with very reduced life expectancy), as well as decreased local tumour control, detrimental effects on the expected treatment response, decreased overall survival and quality of life. Reference Deshwar, Sugar and Torto11–Reference Gobbi, Bergonzi and Comelli14 Lukács et al. Reference Lukács, Kovács and Csanádi12 reported that there is a statistically significant association between shorter delay to presentation with better clinical outcomes, thus early diagnosis and treatment, especially in patients with potentially curable disease would likely improve local control rates and overall survival. The poor prognosis of pancreatic cancer is attributable to late-stage presentation, lack of effective screening and treatments, early recurrence and absence of clinically useful biomarker(s), which can detect the disease in its precursor form(s) or earliest stages. Reference Takayama, Nakagawa and Sawaki4,Reference Rückert, Pilarsky and Grützmann5,Reference Takehara, Eguchi and Ohigashi10,Reference Ballehaninna and Chamberlain15 Consequently, progress in pancreatic cancer requires improved screening for early diagnosis of small or even preinvasive cancers before the onset of metastasis to substantially improve resectability, prognosis after resection as well as new and more effective therapies for improved treatment outcomes and improved survival. In this narrative review paper, we described 13 clinical and emerging biomarkers for pancreatic cancers that could potentially accounts for individual patient variabilities and capable for screening for early detection and diagnosis, to identify patients’ risk for metastatic disease and subsequent relapse, to monitor patient response to specific treatment and to provide clinicians the possibility of prospectively identifying patients who will benefit from a particular treatment. The identification of effective clinical biomarkers that accounts for individual patient variabilities and capable of interrogating key genetic aberrant pathways potentially targetable with molecular targets or immunologic therapies will likely shift the diagnosis and treatment paradigm of pancreatic cancer towards more personalised and targeted medicine.
Materials and Methods
The following databases; PubMed, PMC, NCBI, PNAS, Springer Link, Wiley Online Library, Lacent, Science Direct, Medline were searched from August to December 2020 for relevant studies published in English between 2010 and 2020 and reporting on biomarkers for the management of pancreatic cancer. The literature search used the following keywords: ‘emerging biomarkers and pancreatic cancer’, ‘pancreatic cancer biomarkers’, ‘clinical biomarkers and pancreatic cancer’. The searches were not limited by study design and included conference abstracts, full research articles and reviews. Several publications on biomarkers for the management of pancreatic cancer were identified and we excluded all articles reporting on pancreatic cancers management, but not associated with biomarkers. For the current report, we reviewed articles reporting on emerging and current clinical biomarkers for pancreatic cancer.
Carbohydrate Antigen 19-9 (CA 19-9)
Carbohydrate antigen 19-9 (CA 19-9) is a tumour-associated antigen usually located on the O-glycans on the surface of cells and is synthesised by human pancreatic and biliary ductular cells as well as by gastric, colonic, endometrial and salivary epithelium cells. Reference Bergquist, Puig and Shubert6,Reference Ballehaninna and Chamberlain15–Reference Bauer, El-Rayes and Li17 Several studies have reported that CA 19-9 is expressed in different types of epithelia in many organs of the body, is most commonly associated with identification of pancreas tumours, is capable of identifying the presence of a tumour, but not the type and is one of the preeminent serum biomarkers for pancreatic cancer because of its high sensitivity and specificity. Reference Bergquist, Puig and Shubert6,Reference Ballehaninna and Chamberlain15,Reference Kim, Lee, Lee, Paik, Rhee and Choi16,Reference Ballehaninna and Chamberlain18 The normal range of CA 19-9 detected in humans is between 0 and 37 U/mL and patients with pancreatic cancer usually have elevated levels, although some non-cancerous conditions such as pancreatitis and jaundice can also cause elevated CA 19-9 levels. Reference Bergquist, Puig and Shubert6,Reference Ballehaninna and Chamberlain15–Reference Bauer, El-Rayes and Li17 Kim et al. Reference Kim, Lee, Lee, Paik, Rhee and Choi16 reported that CA 19-9 level is highly elevated in 87% of pancreatic cancer patients and highly correlated to tumour size. Ballehaninna and Chamberlain Reference Ballehaninna and Chamberlain15 reported that serum CA 19-9 level provides vital information on prognosis, overall survival and response to chemotherapy as well as predicts post-operative recurrence. Preoperative serum CA 19-9 level is also reported to provide essential prognostic information in pancreatic cancer patients, correlate with tumour stage and independently predict overall survival. Reference Ballehaninna and Chamberlain15,Reference Ballehaninna and Chamberlain18 According to Ballehaninna and Chamberlain, Reference Ballehaninna and Chamberlain18 preoperative serum levels of CA 19-9 < 37 U/mL are associated with prolonged median survival compared with levels >37 U/mL and levels <100 U/mL implies likely resectable disease, whereas levels >100 U/mL suggest unresectable or metastatic disease. Furthermore, Ballehaninna and Chamberlain, Reference Ballehaninna and Chamberlain15 also reported that increasing post-operative CA 19-9 serum level is associated with poor prognosis and suggest residual disease or the presence of occult metastases, while a decline of post-operative CA 19-9 serum level is associated with improved survival. Ballehaninna and Chamberlain Reference Ballehaninna and Chamberlain15 reported that CA 19-9 is an effective marker for screening, diagnosis, staging and early identification of recurrent cancers and for determining an effective treatment option, although Kim et al. Reference Kim, Lee, Lee, Paik, Rhee and Choi16 indicated that it is more suitable for the identification of late-stage cancers rather than early stages.
Kim et al. Reference Kim, Lee, Lee, Paik, Rhee and Choi16 analysed serum from 70,940 asymptomatic adults and followed those with CA 19-9 serum level above the cut-off value of 37 U/mL to investigate the clinical effectiveness of CA 19-9 as a screening tool for early detection of pancreatic cancer. They reported a sensitivity of 100%, specificity of 98·5% and a positive predictive value of 0·9% for detecting pancreatic cancer in an asymptomatic population. They concluded that on account of the very high sensitivity and specificity of CA 19-9, its screening tests would be more beneficial in symptomatic patients, however, the very low positive predictive value may render it ineffective for mass screening for pancreatic cancer in asymptomatic population. Bergquist et al. Reference Bergquist, Puig and Shubert6 reviewed the National Cancer Database (NCDB 2010–2012) for PDAC patients with reported CA 19-9 results (n = 28,074) to investigate the association of CA 19-9 at diagnosis on survival in anatomically resectable early stage (I and II) pancreatic cancer patients presenting for curative-intent surgery. They reported that elevated levels of CA 19-9 are associated with decreased stage-specific survival in patients (greatest difference observed in early stages), however, neoadjuvant systemic therapy followed by curative-intent surgery mitigated the increased mortality burden. They concluded that, to maximise the effectiveness of preoperative therapeutic triage, all pancreatic cancer patients should have CA 19-9 levels assessed at diagnosis and any level above the normal threshold of 37 U/mL should prompt consideration of systemic chemotherapy in the preoperative setting. Bauer et al. Reference Bauer, El-Rayes and Li17 conducted a study to validate the prognostic value of baseline CA19-9 and the role of its decline from baseline as an early predictive marker for improved outcome in PDAC patients. They pooled data of 50 patients with locally advanced and 162 patients with metastatic PDAC undergoing treatment from 6 prospective trials from 3 different institutions evaluating gemcitabine-containing chemotherapy. They reported a median baseline CA19-9 level of 1,077 ng/mL and reported a median overall survival and median time to progression of 8·7 and 5·8 months, respectively, for patients with CA19-9 levels below the median baseline. Similarly for patients with CA19-9 levels above the median baseline, they reported a median overall survival and median time to progression of 5·2 and 3·7 months, respectively. They concluded that baseline CA19-9 is prognostic for outcome for patients with advanced pancreatic cancer treated with gemcitabine-based regimens and a 5% rise in CA19-9 after two cycles of chemotherapy in the clinical settings serves as a negative predictive marker.
Intercellular Adhesion Molecule-1 (ICAM-1)
The intercellular adhesion molecule-1 (ICAM-1) is a cell-surface-bound glycoprotein belonging to the immunoglobulin superfamily and functions in cell–cell and cell–extracellular matrix adhesion. Reference Mohamed, Saad and Saleh7,Reference Roland, Harken, Sarr and Barnett19 Studies have reported that it plays a physiological role in tight adhesion of leukocytes, acts as a chemoattractant for macrophages, plays a vital role in tumour cell adhesion and progression of metastasis and is a ligand for lymphocyte function-associated antigen 1 (LFA-1) molecule. Reference Mohamed, Saad and Saleh7,Reference Tempia-Caliera, Horvath and Zimmermann8,Reference Roland, Harken, Sarr and Barnett19,Reference Long20 According to Tempia-Caliera et al., Reference Tempia-Caliera, Horvath and Zimmermann8 ICAM-1 is expressed as a chemoattractant on both haematopoietic and non-haematopoietic cells. In haematopoietic cells, it functions in different regions of macrophages, monocytes, activated T-cells, B-cells and lymph nodes, whereas in non-haematopoietic cell surface, it is expressed in vascular endothelial and smooth muscle cells, thymus epithelial cells and fibroblast. Reference Tempia-Caliera, Horvath and Zimmermann8 Furthermore, they reported elevated ICAM-1 expression levels on the surface of different malignant cells including pancreatic cancer cell lines suggesting that its expression influences tumour progression and metastasis. According to Mohamed et al. Reference Mohamed, Saad and Saleh7 and Roland et al., Reference Roland, Harken, Sarr and Barnett19 increased ICAM-1 expression is correlated with poor prognosis in pancreatic cancer.
Mohamed et al. Reference Mohamed, Saad and Saleh7 investigated the sensitivity and specificity of serum ICAM-1 as a biomarker for the diagnosis of early stages of pancreatic cancer. The used serum from 50 patients with histologically diagnosed pancreatic cancer, 27 chronic pancreatitis patients and 35 healthy controls. They reported ICAM-1 sensitivity and specificity of 82 and 82·6%, respectively, to discriminate advanced disease from healthy controls. They concluded that ICAM-1 is an effective biomarker to detect malignant and benign disease, although may not be effective to differentiate between early and late-stage pancreatic cancers. Reference Mohamed, Saad and Saleh7 Tempia-Calera et al., Reference Tempia-Caliera, Horvath and Zimmermann8 studied the distribution, localisation and expression levels of ICAM-1 in 20 pancreatic cancer specimens and 20 normal pancreatic tissues. They observed a 5·4-fold increase of ICAM-1 messenger ribonucleic acid (mRNA) expression level in pancreatic cancer specimens compared with normal controls and reported that normal pancreas do not exhibit immunoreactivity of ICAM-1. They concluded that elevated ICAM-1 expression in human pancreatic cancers plays a role in tumour pathogenesis, may influence the detachment of cancer cells in the primary tumour and contribute to cancer cell migration and metastases.
Myeloid-Derived Suppressor Cells (MDSC)
The MDSCs are a newly identified heterogeneous group of immature myeloid cells characterised by a morphological mixture of granulocytic and monocytic cells, which lack the expression of cell surface markers that are specific to fully differentiated monocytes, macrophages or dendritic cells. Reference Khaled, Ammori and Elkord21–Reference Gabrilovich and Nagaraj27 According to Gabrilovich and Nagaraj, Reference Gabrilovich and Nagaraj27 immature myeloid cells produced in bone marrow rapidly differentiate into mature granulocytes, macrophages or dendritic cells in healthy people. However, in pathological conditions including cancer, there is a partial blockage in the differentiation of immature myeloid cells into mature myeloid cells leading to an increased population of immature myeloid cells. Thus, MDSCs are not present at a steady state in healthy individuals, but are expressed in cancer patients. Reference Gabrilovich and Nagaraj27 Studies have reported that MDSCs are morphologically and phenotypically similar to neutrophils and monocytes, are implicated in pathological conditions including cancer progression and have the potential to suppress various types of immune responses. Reference Thyagarajan, Alshehri, Miller, Sherwin, Travers and Sahu22–Reference Siret, Collignon and Silvy25,Reference Gabrilovich and Nagaraj27 According to Markowitz et al., Reference Markowitz, Brooks and Duggan26 and Gabrilovich and Nagaraj, Reference Gabrilovich and Nagaraj27 the mechanisms employed by MDSCs to be immunosuppressive and function to inhibit the immune response to cancer include the depletion of nutrients from tumour microenvironments, the production of reactive oxygen and nitrogen species with the potential to inhibit key immunologic pathways, secretion of immune-suppressive cytokines and the induction of inhibitory immune cells. Trovato et al. Reference Trovato, Fiore and Sartori28 reported that PDAC cells release pro-inflammatory metabolites that induce pronounced alteration of normal haematopoiesis thereby favouring the expansion and accumulation of MDSCs and according to Thyagarajan et al. Reference Thyagarajan, Alshehri, Miller, Sherwin, Travers and Sahu22 MDSCs aid the development of PDAC and also hamper the antitumour immune responses induced by some therapeutic agents. According to Siret et al. Reference Siret, Collignon and Silvy25 and Markowitz et al., Reference Markowitz, Brooks and Duggan26 elevated levels of MDSCs in the peripheral circulation of pancreatic cancer patients is correlated to the extent of disease, with stage and is also associated with poor prognosis.
Several studies have demonstrated a positive correlation between elevated levels of MDSC and progression of PDAC. Reference Thyagarajan, Alshehri, Miller, Sherwin, Travers and Sahu22,Reference Markowitz, Brooks and Duggan26,Reference Rajabinejad, Salari, Gorgin Karaji and Rezaiemanesh29 Markowitz et al. Reference Markowitz, Brooks and Duggan26 analysed mononuclear cells isolated from serum from 13 patients receiving chemotherapy, 15 chemonaive patients and 9 healthy controls to determine if MDSC levels in peripheral blood is elevated in patients with progressive PDAC. They reported significantly lower MDSC levels in the peripheral blood of patients with stable pancreatic cancer compared to patients with progressive disease and a cut-off value of 2·5 % MDSC identified patients with progressive disease. Furthermore, they observed an association between poor Eastern Cooperative Oncology Group (ECOG) performance status and increased serum levels of MDSC in patients. They concluded that MDSC level in peripheral blood is a potential predictive biomarker of chemotherapy failure in pancreatic cancer patients. Reference Markowitz, Brooks and Duggan26 Trovato et al. Reference Trovato, Fiore and Sartori28 used flow cytometry to determine the frequency of MDSC in peripheral blood in 3 independent cohorts of 117 PDAC patients and also evaluated the frequency of tumour-infiltrating MDSC and the immune landscape in fresh biopsies. They reported that the frequency of circulating MDSCs is significantly associated with shorter overall survival and metastatic disease and concluded that MDSC analysis can aid to define the immune landscape of PDAC patients for more appropriate diagnosis, stratification and treatment. Porembka et al. Reference Porembka, Mitchem and Belt30 investigated the prevalence and significance of MDSC in PDAC using peripheral blood, bone marrow and tumour samples collected from pancreatic cancer patients and cancer-free controls. They also assessed the suppressive capability of MDSC and the effectiveness of MDSC depletion in C57BL/6 mice model. They reported increased frequency of MDSC in bone marrow and peripheral blood of pancreatic cancer patients and correlated with disease stage, however, normal pancreatic tissue showed no MDSC infiltrate. Furthermore, they reported that both human and murine tumours recruited MDSC that suppressed CD8+ T cells and accelerated tumour growth, however, treating with zoledronic acid halted intratumoural MDSC accumulation and resulted in delayed tumour growth rate, prolonged median survival and increased recruitment of T cells to the tumour. They concluded that MDSCs are essential mediators of tumour-induced immunosuppression in pancreatic cancer and inhibiting its accumulation with zoledronic acid improves antitumour response in animal studies suggesting that any technique that blocks MDSC may be a potential novel treatment strategy for pancreatic cancer.
Laminin γ2 (LAMC2)
The laminins are a family of large heterotrimeric multidomain glycoproteins consisting of α-chain, β-chain and γ-chain subunits and exist in five, four and three genetically distinct forms, respectively. Reference Domogatskaya, Rodin and Tryggvason31,Reference Katayama, Sanzen, Funakoshi and Sekiguchi32 Several studies have reported that laminins influence cell function by inducing various signalling pathways via cell membrane receptors, function to provide apoptotic resistance as well as influence cell-type-specific growth and development processes such as adhesion, differentiation, migration, morphogenesis and phenotype maintenance. Reference Domogatskaya, Rodin and Tryggvason31,Reference O’Leary, Wright and Brister33–Reference Garg, Braunstein and Koeffler36 Laminin-5 is one isoform of the laminin family, which consist of the laminin α3 (LAMA3), β3 (LAMB3) and γ2 (LAMC2) chain subunits and normally functions as an essential adhesive component of the epithelial basement membrane by acting as a cell adhesive ligand for cell surface integrins. Reference Domogatskaya, Rodin and Tryggvason31,Reference Katayama, Funakoshi, Sumii, Sanzen and Sekiguchi35–Reference Takahashi, Hasebe and Oda38 The laminin-5 regulates cell adhesion, differentiation, migration and the invasion of epithelial cells in normal tissues and its aberrant expression has been associated with tumour invasion and metastasis. Reference Domogatskaya, Rodin and Tryggvason31,Reference Garg, Braunstein and Koeffler36–Reference Takahashi, Hasebe and Oda38 The LAMC2 protein is found exclusively in laminin-5 and it’s encoded by the LAMC2 gene located on the long arm of chromosome 1 at position 25·3 (1q25·3). Reference O’Leary, Wright and Brister33,Reference Chan, Prassas and Dimitromanolakis34,Reference Garg, Braunstein and Koeffler36 Kosanam et al. Reference Kosanam, Prassas and Chrystoja39 and Wang et al. Reference Wang, Cai, Du, Wei and Shen37 reported that LAMC2 and its receptors are highly upregulated in pancreatic cancers and its co-overexpression with phosphorylated protein kinase B (AKT) is associated with poor prognosis and Uhlen et al. Reference Uhlen, Zhang and Lee40 have also reported LAMC2 overexpression in PDAC. Several studies have reported that LAMC2 expression is associated with tumour invasion and metastasis and elevated levels are correlated with poor overall survival and early recurrence. Reference Garg, Braunstein and Koeffler36–Reference Takahashi, Hasebe and Oda38 According to Garg et al., Reference Garg, Braunstein and Koeffler36 serum levels of LAMC2 is elevated in pancreatic cancer patients who have low serum levels of CA 19-9 suggesting that serum measurement of both LAMC2 and CA 19-9 levels can potentially provide a more sensitive technique for the detection of pancreatic cancer.
Wang et al. Reference Wang, Cai, Du, Wei and Shen37 investigated the expression patterns of LAMC2 and sodium–hydrogen antiporter 1 (NHE1) in pancreatic cancer and the mechanisms involved in LAMC2/AKT/NHE1 signalling for pancreatic tumour invasion. They reported that activation of AKT signalling by LAMC2 leads to overexpression and activation of NHE1, which induces an acidic tumour microenvironment that disrupts normal cell physiology and enhances pancreatic cancer cells’ invasion. However, they observed that application of LY294002 (a PI3K inhibitor) and/or ethyl-isopropyl amiloride (EIPA, an NHE1 inhibitor) disrupted aberrant LAMC2/AKT/NHE1 signalling. They concluded that LAMC2 has the potential as a novel prognostic and therapeutic agent for the treatment of pancreatic cancer. Kosanam et al. Reference Kosanam, Prassas and Chrystoja39 also investigated the potential of LAMC2 as an early stage diagnostic serological biomarker for pancreatic cancer by analysing serum samples from healthy, benign and early and late-stage cancer patients from three geographically diverse regions [Japan (n = 150), Europe (n = 200) and the USA (n = 85)]. They observed significantly elevated levels of LAMC2 in early stage and late-stage PDAC compared to benign and normal diseases and reported that a combined biomarker panel of LAMC2 and CA 19-9 levels has better potential, than CA-19-9 alone, to discriminate between age-matched normal and benign patients from PDAC patients. They concluded that LAMC2 holds promise to increase early stage diagnosis, monitor therapeutic response in CA-19-9-negative patients and is an important complementary biomarker for CA-19-9. Chan et al. Reference Chan, Prassas and Dimitromanolakis34 performed a retrospective blinded assessment of serum samples from 250 PDAC patients at various disease stages, 130 benign disease patients and 20 healthy individuals to identify potential early detection markers of PDAC and to develop a biomarker panel that could discriminate PDAC from other benign diseases. They reported that a biomarker panel of serum CA-19-9, CA 125 and LAMC2 has a significant potential to discriminate early stage PDAC from benign conditions and chronic pancreatitis. Garg et al. Reference Garg, Braunstein and Koeffler36 conducted a review assessing current knowledge of LAMC2 and observed that its molecular role in tumourigenesis, growth, invasion and metastasis suggest that LAMC2 may be a potential anticancer therapeutic target with inhibition via neutralising monoclonal antibodies. Furthermore, they reported that LAMC2 could be a good serum diagnostic biomarker, but indicated the need for more studies with larger and more diverse cohorts to better understand its diagnostic efficacy. Takahashi et al. Reference Takahashi, Hasebe and Oda38 conducted an immunohistochemical analysis on 48 post-operative PDAC patients and reported that cytoplasmic expression of LAMC2 is primarily observed in metastatic tumour cells and is strongly correlated with poorer overall survival of PDAC.
Carcinoembryonic Antigen (CEA)
The carcinoembryonic antigen (CEA) family consists of a heterogeneous group of glycoproteins with a molecular weight of 180–200 kDa and is involved in cell adhesion. Reference Lee and Lee41,Reference Meng, Shi and Liang42 CEA is normally produced in gastrointestinal tissue during foetal development, however, the production terminates before birth and it is therefore usually present at very low levels in the blood of healthy adults. Reference Meng, Shi and Liang42–Reference Imaoka, Mizuno and Hara44 According to Lee and Lee, Reference Lee and Lee41 the human CEA gene family consist of 29 genes or pseudogenes and based on sequence similarities and functions can be divided into the CEA-related cell adhesion molecule (CEACAM), pregnancy-specific glycoprotein (PSG) and pseudogene groups. Gan et al. Reference Gan, Jia and Zheng43 reported that the normal range of CEA measured in the blood of a non-smoker adult is <2·5 ng/mL and <5·0 ng/mL in a smoker adult. Several studies have reported elevated levels of CEA in pancreatic tumours, pancreatic juice and serum of pancreatic cancer patients. Reference Meng, Shi and Liang42,Reference Imaoka, Mizuno and Hara44–Reference Lee, Yi and Chung47 According to Meng et al. Reference Meng, Shi and Liang42 and Imaoka et al., Reference Imaoka, Mizuno and Hara44 serum level of CEA is elevated in about 30–60% of pancreatic cancer patients and Hu et al. Reference Hu, Kaushal and Cao45 reported CEA over expression in about 90% of pancreatic tumours. Meng et al. Reference Meng, Shi and Liang42 have reported that elevated levels of serum CEA is an independent predictor of poor survival, are significantly related to poor prognosis and could play an important role in predicting survival of pancreatic cancer patients. Moreover, the utilisation of a panel of CEA with CA19-9, CA-125 and CA50 would potentially increase the accuracy in distinguishing pancreatic cancer patients from healthy individuals. Reference Meng, Shi and Liang42 According to Imaoka et al., Reference Imaoka, Mizuno and Hara44 elevated serum levels of CEA is a potential tumour biomarker for monitoring patients after surgery and for assessing the effectiveness of chemotherapy.
Lee et al. Reference Lee, Yi and Chung47 conducted a retrospective review of the medical records of 187 PDAC patients treated with either surgery, chemoradiotherapy or chemotherapy to establish the potential value of CEA as a prognostic marker to determine survival in PDAC patients. They observed elevated serum levels of CEA in 39% of patients at diagnosis, 33% of patients with resectable pancreatic cancer and 47% of patients with advanced pancreatic cancer. They reported that CEA is correlated with tumour stage and patients with elevated serum levels of CEA have shorter overall survival compared to those with normal serum CEA levels. They concluded that patients with elevated serum CEA level at diagnosis have poor overall survival and pretreatment CEA level may predict the prognosis of patients with pancreatic adenocarcinoma. Poruk et al. Reference Poruk, Gay and Brown48 reviewed data from 23 studies representing 1,324 patients with pancreatic cancer and 9 studies representing 301 cases with benign pancreatic disease to re-evaluate the accuracy of CEA for the diagnosis of PDAC and its potential to discriminate malignant and benign disease. They reported mean sensitivity and specificity for CEA of 44 and 85%, respectively, for detection of PDAC. Furthermore, they reported that the accuracy of CEA levels to discriminate malignant and benign disease using a threshold value of 5 ng/mL has a sensitivity of 45% and a specificity of 85%. They concluded that using a CEA cut-off value of 5·0 ng/mL in patients exhibiting signs and symptoms suspicious for PDAC has high enough specificity to aid in clinical diagnosis. Imaoka et al. Reference Imaoka, Mizuno and Hara44 conducted a retrospective study reviewing data from 433 patients with metastatic pancreatic cancer to investigate the potential value of CEA levels as a prognostic biomarker. They reported that patients with elevated (> 5 ng/mL) CEA levels has a significantly shorter median overall survival compared with those with normal CEA (≤ 5 ng/mL) levels, CEA level is an independent predictive factor for overall survival, and an independent prognostic factor in patients with metastatic pancreatic cancer. They concluded that a combination chemotherapy regimen may offer modest survival benefit in patients with high CEA.
Tissue Inhibitor of Metalloproteinases-1 (TIMP-1)
The tissue inhibitors of metalloproteinases (TIMPs) are tissue-specific, endogenous inhibitors of the matrix metalloproteinases (MMPs) including the closely related disintegrin and metalloproteinases (ADAMs) and ADAMs with thrombospondin motifs (ADAMTSs). Reference Arpino, Brock and Gill49,Reference Brew and Nagase50 Brew and Nagase Reference Brew and Nagase50 and Arpino et al. Reference Arpino, Brock and Gill49 reported that the TIMPs family consist of four homologous members, namely TIMP-1, TIMP-2, TIMP-3 and TIMP-4 and are involved in various biological activities such as promoting cell proliferation and cell migration; and in anti-angiogenic, pro- and anti-apoptotic and synaptic plasticity activities. According to Brew and Nagase Reference Brew and Nagase50 and Stocum, Reference Stocum51 the TIMP-1 protein, which is a small 28-kD glycoprotein is encoded by the TIMP-1 gene located on the short arm of chromosome X at position 11·3 (Xp11·3) and it is upregulated during histolysis. Several studies have reported that TIMP-1 regulates the degradation of extracellular matrix proteolysis in healthy tissues, mediate angiogenesis through interaction with β1 integrin and CD63 and its expression is elevated in many pathological conditions including PDAC. Reference Arpino, Brock and Gill49,Reference Brew and Nagase50,Reference Crawford, Bioulac-Sage and Hytiroglou52–Reference D’Costa, Jones and Azad55 According to Prokopchuk et al., Reference Prokopchuk, Grünwald and Nitsche54 plasma and tissue TIMP-1 expression is significantly elevated in early pancreatic lesions such as chronic pancreatitis, in pancreatic intraepithelial neoplasia and in late PDAC patients suggesting its potential prognostic and diagnostic value for PDAC. Furthermore, TIMP-1 expression has been associated with tumour progression, positively correlated with the degree of desmoplasia in tumour stroma and with de-differentiation of pancreatic tumour cells and elevated levels in tumour tissue and in peripheral blood is associated with poor clinical outcome in numerous malignancies. Reference Prokopchuk, Grünwald and Nitsche54
Poruk et al. Reference Poruk, Firpo and Scaife53 analysed serum from 86 PDAC patients, 86 healthy controls and 48 chronic pancreatitis patients to investigate the potential of serum TIMP-1 to detect early stage disease and its ability to discriminate PDAC and chronic pancreatitis patients and healthy controls. They also evaluated the diagnostic accuracy of TIMP-1 in comparison to CA19-9 and the potential of TIMP-1 as a prognostic marker to predict survival in pancreatic cancer patients. They reported that serum levels of TIMP-1 could discriminate PDAC from chronic pancreatitis patients and healthy individuals and could also distinguish early stage, resectable PDAC patients from chronic pancreatitis and healthy control. They concluded that serum TIMP-1 has a potential application as a diagnostic biomarker in PDAC and the utilisation of osteopontin (OPN), TIMP-1 and CA 19-9 panel can potentially improve the diagnostic accuracy in PDAC. Prokopchuk et al., Reference Prokopchuk, Grünwald and Nitsche54 conducted a retrospective investigation in 36 PDAC patients, 25 chronic pancreatitis patients and 13 controls to determine the potential association of TIMP-1 levels with 2 PDAC-associated conditions (cachexia and jaundice) and also the diagnostic and prognostic value of TIMP-1 in chronic pancreatitis and PDAC patients. They observed elevated plasma TIMP-1 levels in chronic pancreatitis and PDAC patients with concomitant jaundice or cachexia. They reported that elevated levels of TIMP-1 is associated with clinical cachexia markers including weight loss and lung function, as well as ferritin, haemoglobin and cholinesterase levels and significantly correlated with cachexia only in patients without jaundice. They concluded that plasma levels of TIMP-1 are correlated with pancreatic lesion-induced cachexia in patients without jaundice and it is counter-indicated as a survival marker in patients with jaundice, however, combining TIMP-1 with cachexia represents a promising combination of prognostic parameters. Reference Prokopchuk, Grünwald and Nitsche54 D’Costa et al. Reference D’Costa, Jones and Azad55 also investigated the oncogenic role of TIMP-1 in both primary pancreatic and metastatic tumours treated with gemcitabine chemotherapy in both in vitro and animal models. They observed that TIMP-1 is directly elevated in response to gemcitabine treatment that is mainly related to a pro-tumourigenic phenotype. Furthermore, they reported that TIMP-1 is upregulated in pancreatic intraepithelial neoplasias grade 3 and PDAC lesions compared to matched normal pancreatic tissue and it plays a role in tumour clonogenic survival and vascular density, however, inhibiting TIMP-1 resensitised tumours to gemcitabine and radiotherapy. They concluded that TIMP-1 upregulation as a resistance mechanism to gemcitabine provides a rationale for combining chemoradiotherapy with TIMP-1 inhibitors for PDAC patients.
Mucin-16 (MUC16)
The mucins (MUCs) are a family of large extensively glycosylated proteins with a heavily O-glycosylated tandem repeat region that is rich in proline, threonine and serine residues. They function as a coating lining that protects the mucosal surface, moisturising materials, lubricants and reducer of surface tension as well as antimicrobial reagents and ion-exchange polymers. Reference Kufe56–Reference Chen, Hung, Wang, Paul and Konstantopoulos59 The human mucin family consists of 21 members designated as MUC1 to MUC21 and based on their physiological and structural characteristics are further sub classified into secreted MUCs (MUC2, MUC5AC, MUC5B, MUC6, MUC7 and MUC19) and transmembrane mucins (MUC1, MUC3A/B, MUC4, MUC11-MUC13, MUC15–MUC17, MUC20 and MUC21). Reference Kufe56,Reference Chen, Hung, Wang, Paul and Konstantopoulos59,Reference Kaur, Kumar, Momi, Sasson and Batra60 According to Kaur et al., Reference Kaur, Kumar, Momi, Sasson and Batra60 the mucin genes are highly polymorphic due to varying numbers of tandem repeats as evidenced by the wide difference in expression profiles of both transmembrane (MUC1, MUC3, MUC4, MUC7, MUC13, MUC16 and MUC17) and secretory MUCs (MUC5AC, MUC5B and MUC6) in comparison between healthy pancreas and pancreatic cancers as well as in comparison between different stages of disease progression. Furthermore, aberrant changes in mucin expression are also the characteristic event in early lesions of pancreatic mucinous cystic neoplasms. Reference Kaur, Kumar, Momi, Sasson and Batra60 Mucin-16 [MUC16, sometimes used interchangeably with cancer antigen 125 (CA-125)] is a transmembrane mucin that is overexpressed in about 65% of malignant pancreatic cancers with elevated expression in early stage and metastatic PDACs. Reference Chen, Hung, Wang, Paul and Konstantopoulos59–Reference Das and Batra63 The MUC16 gene is located on the short arm of chromosome 19 at position 13·2 (19p13·2) and encodes the MUC16 protein, which contains an extracellular N terminus adjacent to glycosylated tandem repeats, a transmembrane region and a short cytoplasmic tail. Reference Chen, Dallas, Balzer and Konstantopoulos58,Reference Haridas, Chakraborty and Ponnusamy61,Reference Das and Batra63,Reference Aithal, Rauth and Kshirsagar64 The ability of MUC16 to alter tumour cell interactions with its microenvironment has been implicated in tumourigenesis, tumour invasion and metastasis. Reference Chen, Hung, Wang, Paul and Konstantopoulos59–Reference Haridas, Chakraborty and Ponnusamy61,Reference Aithal, Rauth and Kshirsagar64 Chen et al. Reference Chen, Dallas, Balzer and Konstantopoulos58 reported that MUC16 is not expressed in normal pancreatic ducts but is strongly upregulated in pancreatic cancer which suggests its potential role in disease progression. Furthermore, they observed that MUC16 expression is strongly associated with poor survival, poor prognosis and unfavourable outcome for pancreatic cancer patients. Reference Chen, Hung, Wang, Paul and Konstantopoulos59 According to Aithal et al., Reference Aithal, Rauth and Kshirsagar64 aberrant MUC16 overexpression has been observed in pancreatic cancers and as a result of its functional involvement in tumour development, MUC16 and its ligands have emerged as potential targets for therapeutic intervention with monoclonal antibodies and immunotherapy. Das and Batra Reference Das and Batra63 reported that some novel therapeutic approaches include prevention of MUC16 cleavage, disruption of MUC16-ligand binding and disruption of MUC16 secretory pathway.
Haridas et al. Reference Haridas, Chakraborty and Ponnusamy61 investigated the differential expression of MUC16 during pancreatic cancer development and progression as well as the correlation between MUC16 expression and tumour characteristics such as stage, grade and metastasis. They observed that MUC16 is not expressed in normal pancreatic ducts but is detected in pancreatitis tissue and also upregulated in metastatic lesions suggesting its role in disease metastasis. Furthermore, they reported that MUC16 expression increases progressively with loss of tumour differentiation and are detected in high-grade preneoplastic lesions preceding invasive adenocarcinoma, which suggest that its upregulation is a late event during the initiation of disease. They concluded that MUC16 expression is significantly elevated in pancreatic cancer and plays a potential role in the progression of the disease. Einama et al. Reference Einama, Kamachi and Nishihara65 investigated the prognostic value and the clinicopathological implication of mesothelin (MSLN) and MUC16 co-expression in 66 PDAC tissue samples by immunohistochemical analysis. They observed that the co-expression of MSLN and MUC16 are strongly correlated, is associated with higher histological grade and blood vessel invasion, is associated with poor patient outcome compared to high MSLN or MUC16 expression alone and correlated with liver metastases. Furthermore, they reported that high expression of MUC16 is highly correlated with pancreatic cancer recurrence, worse relapse-free survival and overall survival. They concluded that MSLN and MUC16 are co-expressed in PDAC and the co-expression is associated with poor prognosis and invasive tumours and has the potential as a useful predictor for pancreatic cancer aggressiveness. Moreover, MSLN and MUC16 could be useful prognostic markers and potential molecular treatment targets to improve pancreatic cancer clinical outcomes. Reference Einama, Kamachi and Nishihara65 Chen et al. Reference Chen, Hung, Wang, Paul and Konstantopoulos59 also investigated the mechanism of MSLN-MUC16 molecular interactions in pancreatic cancer cell motility and invasion using immunopurification, immunoblotting transwell invasion assay and microfluidic-based cell migration assay. They demonstrated that MSLN binding to MUC16 expressed by metastatic pancreatic cancer cells enhances their motility and invasive potential by selectively upregulating matrix metalloproteinase 7 (MMP-7) via a p38 mitogen-activated protein kinase (MAPK)-dependent pathway. They reported that their findings provide a novel perspective on the enhanced invasive potential associated with MSLN and MUC16 co-overexpression as well as the mechanism underlying MMP-7 activation in pancreatic cancer invasion and metastasis. They concluded that the co-overexpression of MSLN and MUC16 may facilitate early local invasion of pancreatic cancer cells via activation of MMP-7 and MSLN and MUC16 may be potential therapeutic targets for the treatment of metastatic pancreatic cancer.
Plectin-1 (PLEC1)
Plectin is an intracellular linker protein of the cytoskeleton and a member of the plakin family of cytolinker proteins, which acts as a link between the three main components of the cytoskeleton, namely the actin microfilaments, microtubules and intermediate filaments. Reference Castañón, Walko, Winter and Wiche66 Plectin is reported to be expressed in the epithelial lining of the gastrointestinal tract and endothelial cells of vessels, and are useful in identifying cancers in the oesophagus, stomach, lungs, pancreas and the oral cavity. Reference Castañón, Walko, Winter and Wiche66,Reference Konkalmatt, Deng and Thomas67 According to Liu et al., Reference Liu, Maercker, Castanon, Hauptmann and Wiche68 the Plectin-1 (PLEC1) gene is located on the long arm of chromosome 8 at position 24·3 (8q24·3) and encodes the Plectin-1 protein. Several investigators Reference Bausch, Thomas and Mino-Kenudson9,Reference Kelly, Bardeesy and Anbazhagan69,Reference Bausch, Mino-Kenudson, Fernández-del Castillo, Warshaw, Kelly and Thayer70 have reported that PLEC1 is highly expressed in invasive pancreatic cancer, can potentially distinguish malignant pancreatic disease from chronic pancreatitis and is effective at detecting PADCs at early stages before the cancer invades into other areas of the body. Bausch et al. Reference Bausch, Thomas and Mino-Kenudson9 have reported that 93% of PDAC cases are PLEC1 positive and its overexpression on cell surfaces of PDACs provides new information about the development of pancreatic cancer that could eventually lead to new techniques to treat the disease. According to Bausch et al., Reference Bausch, Mino-Kenudson, Fernández-del Castillo, Warshaw, Kelly and Thayer70 PLEC1 is highly specific and sensitive to early and invasive cancer and its overexpression increases during pancreatic carcinogenesis. Other investigators Reference Bausch, Thomas and Mino-Kenudson9,Reference Konkalmatt, Deng and Thomas67,Reference Kelly, Bardeesy and Anbazhagan69,Reference Chen, Zhou and Li71 have also exploited PLEC1 overexpression in PDAC patients for non-invasive imaging of PDAC and its metastases.
Bausch et al. Reference Bausch, Thomas and Mino-Kenudson9 investigated the suitability of PLEC1 as a marker to detect PDAC at an early stage using human PDAC, chronic pancreatitis and normal pancreata specimens evaluated by immunohistochemistry and Western blot analysis. They also assessed the useability of PLEC1 as imaging targets in preclinical orthotopic and liver metastasis murine models of PDAC. They reported PLEC1 expression positivity in all PDACs samples but none in benign tissues and the expression level increases during pancreatic carcinogenesis. Furthermore, they observed that PLEC1 expression is retained in all metastatic foci assayed and clearly highlighted the metastatic deposits in lymph nodes, liver and peritoneum. In addition, they reported that in vivo imaging using PLEC1 targeting peptides specifically highlighted the primary and metastatic tumours. They concluded that PLEC1 can discriminate malignant pancreatic disease from chronic pancreatitis, PLEC1 targeted imaging of PDAC is feasible and could potentially detect preinvasive pancreatic intraepithelial neoplasia 3 (PanIN3) lesions. Furthermore, they suggested that the clinical use of PLEC1-based imaging should permit the early diagnosis of small or preinvasive cancers and metastatic disease, thereby leading to improved resectability rates and patients’ survival. Konkalmatt et al. Reference Konkalmatt, Deng and Thomas67 conducted a study to demonstrate that genetically re-engineered AAV2 vector bearing PLEC1 Targeting Peptide (AAV-PTP) preferentially target gene delivery to PDAC cells in nude mice bearing pancreatic tumour xenografts. They observed that the AAV-PTP preferentially targeted the human PDAC cell lines over the non-neoplastic human pancreatic cell lines thereby establishing the potential of PTP-modified AAV capsids to selectively target gene delivery to PDAC cells, and therefore hold promise as a new strategy for the early detection, diagnosis and treatment of pancreatic cancer. Bausch et al. Reference Bausch, Mino-Kenudson, Fernández-del Castillo, Warshaw, Kelly and Thayer70 evaluated whether PLEC1 expression is a potential specific marker for malignant pancreatic intraductal papillary mucinous neoplasms (IPMN) and also if it can be exploited to identify metastatic foci in lymph nodes. They used immunohistochemistry to assay PLEC1 expression in 6 benign dysplasia, 31 malignant IPMN dysplasia and 12 lymph node metastases from carcinoma arising in IPMN. They reported PLEC1 positivity in 84% (26 of 31) of malignant IPMN and all 12 lymph node metastases, but only 1 of the 6 benign IPMN expressed PLEC1. Furthermore, they reported a specificity and sensitivity of 83 and 84%, respectively, of PLEC1 in discriminating malignant IPMN from benign IPMN and concluded that PLEC1 is an excellent biomarker for the early detection of carcinoma arising in IPMN.
Regenerating Islet-Derived Protein 4 (REG4)
The regenerating islet-derived (REG) protein family is made of C-type lectin-like secreted proteins that are reported to play a role in tissue regeneration and inflammation in digestive organs. Reference Takayama, Nakagawa and Sawaki4,Reference Parikh, Stephan and Tzanakakis72,Reference Ma, Wu, Zhous, Wan, Lui and Xu73 The expression levels of members of the REG family are reported to be upregulated in several gastrointestinal cancers and function as trophic or anti-apoptotic factors in cancers. Reference Takayama, Nakagawa and Sawaki4,Reference Takehara, Eguchi and Ohigashi10 According to Legoffic et al., Reference Legoffic, Calvo and Cano74 five structurally related REG members have been identified in humans and are stratified into three subclasses, namely REG1A and REG1B (Type 1), REG3A and REG3G (Type 3) and REG4 (Type 4), which are based on the primary structures of the encoded proteins. The REG4 protein is encoded by the REG4 gene located on the short arm of chromosome 1 at position 12 (1p12) Reference Legoffic, Calvo and Cano74 and it is highly expressed in poorly differentiated pancreatic cancer cells, but insignificantly expressed in well-differentiated pancreatic cancer cells. Reference Takehara, Eguchi and Ohigashi10,Reference Ma, Wu, Zhous, Wan, Lui and Xu73,Reference Legoffic, Calvo and Cano74 According to Ma et al., Reference Ma, Wu, Zhous, Wan, Lui and Xu73 REG4 has been observed to play a significant role in the aggressiveness of PDAC by promoting both proliferation and invasion of pancreatic cancer cells. Legoffic et al. Reference Legoffic, Calvo and Cano74 has reported that REG4 is present in increased copy number in pancreatic cancer cells and in late precancerous pancreatic lesions. Furthermore, Takayama et al. Reference Takayama, Nakagawa and Sawaki4 has also observed elevated levels of REG4 in serum of pancreatic cancer patients and reported that REG4 is a good marker to discriminate pancreatic cancer patients from health individuals. Several studies on xenografted pancreatic cancer cell lines have demonstrated that REG4 overexpression stimulates tumour growth, however, blocking circulating REG4 protein with a specific antibody would potentially inhibit tumour proliferation. Reference Takayama, Nakagawa and Sawaki4,Reference Takehara, Eguchi and Ohigashi10,Reference Legoffic, Calvo and Cano74
Legcoffic et al. Reference Legoffic, Calvo and Cano74 conducted a study to identify the specific genes that are altered in the early stages of pancreatic adenocarcinoma development. They observed overexpression of REG4 in both pancreatic cancer and PanIN3 precancerous lesions. Furthermore, they reported that REG4 overexpression stimulates cell growth, increases tumourigenicity and enhances resistance to gemcitabine treatment, however, systemic treatment with an antibody against REG4 decreases tumourigenicity. They concluded that adjuvant therapies targeting REG4 expression could improve the standard treatment of pancreatic cancer with gemcitabine. Ma et al. Reference Ma, Wu, Zhous, Wan, Lui and Xu73 investigated the mechanisms by which tumour cells educate and reprogram tumour-associated macrophages (TAMs). They reported that REG4 overexpression in PDAC promotes macrophage polarisation to M2 phenotype and also changes the microenvironment to facilitate cancer growth and metastasis. Takayama et al. Reference Takayama, Nakagawa and Sawaki4 conducted a study to evaluate the effectiveness of REG4 for the detection of pancreatic cancer using pre-therapeutic sera from 92 pancreatic cancer patients, 28 patients with other pancreatic tumours, 11 patients with pancreatitis and 69 healthy controls. They observed elevated serum levels of REG4 expression in pancreatic cancer patients compared to healthy controls and reported a sensitivity, specificity and accuracy of REG4 for pancreatic cancer of 95, 64 and 78%, respectively, at a cut-off value of 3·49 ng/mL. Furthermore, they reported that REG4 is capable of discriminating pancreatic cancer patients from healthy individuals. They concluded that serum levels of REG4 is a valuable marker to discriminate pancreatic cancer patients from healthy individuals and holds potential for cancer screening for both late and early disease stages. Takehara et al. Reference Takehara, Eguchi and Ohigashi10 also investigated serum REG4 as a screening method to detect early stage PDAC and the development of novel molecular therapies for PDAC treatment using preoperative and post-operative serum samples from 11 patients who had curative resection and 31 PDAC tissue samples. They reported significant elevation of REG4 expression in the serum of patients with early stage PDAC and a monoclonal antibody against REG4 decreases tumourigenicity. They concluded that REG4 is a potential tumour marker to screen early stage PDAC, and blocking REG4 expression with an antibody may offer a novel potential strategy for the treatment of PDAC.
Glypican-1 (GPC1)
Glypicans are membrane-bound proteins that are members of the heparan sulfate proteoglycan (HSPG) families and are highly expressed on cell membranes and in the extracellular matrix. They are involved in organ development through modulation of extracellular growth signals, implicated in morphogen gradient formation, human overgrowth and skeletal dysplasia disorders. Reference Wang, Qiu and Bai75–Reference Herreros-Villanueva and Bujanda80 Various studies have reported that the human genome encompasses six glypicans (GPC1–GPC6), which are highly expressed in cancer cells and are potentially associated with tumourigenesis, angiogenesis, invasion and metastasis. Reference Wang, Qiu and Bai75,Reference Lu, Niu, Liu, Gao, Sun and Zhao76,Reference Melo, Luecke and Kahlert79 According to Wang et al., Reference Wang, Qiu and Bai75 GPC1 levels are detectable in peripheral blood of cancer patients, and therefore holds a great promise as a new glypican biomarker in oncology. Several studies have reported that GPC1 is predominantly expressed in the central nervous system, skin, skeletal system, kidney and testis during embryonic development, but there is little or no expression in the pancreas, liver, lung and blood cells. Reference Wang, Qiu and Bai75,Reference Lu, Niu, Liu, Gao, Sun and Zhao76,Reference Herreros-Villanueva and Bujanda80 However, it is also reported that GPC1 is significantly overexpressed at both the mRNA and protein levels in PDAC and might play an important role in the initiation and progression of the disease. Reference Lu, Niu, Liu, Gao, Sun and Zhao76,Reference Qian, Tan, Zhang, Yang and Li77,Reference Melo, Luecke and Kahlert79 According to recent studies, the downregulation of GPC1 can potentially decrease tumourigenicity, differentiation, angiogenesis, neurodegeneration of pancreatic cancer cells and tumour development. Reference Wang, Qiu and Bai75–Reference Qian, Tan, Zhang, Yang and Li77,Reference Frampton, Prado and López-Jiménez81 However, elevated levels of GPC1 is reported to be significantly correlated with pathologic grades, clinical stage, cancer progression, perineural invasion and closely associated with poor prognosis of patients with pancreatic cancer. Reference Wang, Qiu and Bai75,Reference Lu, Niu, Liu, Gao, Sun and Zhao76,Reference Hasan, Jacob, Manne and Paluri78,Reference Melo, Luecke and Kahlert79
Qian et al. Reference Qian, Tan, Zhang, Yang and Li77 investigated whether GPC1 detection in extracellular vesicles is a predictor of outcome of regional intra-arterial chemotherapy (RIAC) for patients with advanced pancreatic cancer. They isolated extracellular vesicles from the plasma of 28 advanced pancreatic cancer patients before and after RIAC therapy and 16 age- and gender-matched healthy individuals. They reported significantly elevated levels of GPC1-positive extracellular vesicles in patients with advanced pancreatic cancer compared with healthy individuals, however, the proportion decreased after RIAC therapy. Furthermore, they observed improved overall survival rates in patients exhibiting a greater decrease of GPC1-positive extracellular vesicles and concluded that GPC1 is a potential novel prognostic biomarker for patients with advanced pancreatic cancer undergoing RIAC therapy. Kleeff et al. Reference Kleeff, Ishiwata and Kumbasar82 also investigated the role of GPC1 in the proliferative responses of pancreatic cancer cells using 16 pancreatic cancers, 14 chronic pancreatitis and 12 normal pancreatic tissue samples. They observed that human pancreatic cancers overexpress GPC1 at both the mRNA and protein levels, whereas its expression level is low in normal pancreas and in chronic pancreatitis reported that GPC1 may play an important role in neoplastic transformation and pancreatic cancer progression. Melo et al. Reference Melo, Luecke and Kahlert79 investigated the detection of GPC1-positive circulating exosomes using serum from 190 PDAC patients and 100 healthy donors. They reported significant elevation of GPC1-positive circulating exosomes in the serum of patients with pancreatic cancer with 100% specificity and sensitivity and could distinguish healthy individuals and patients with benign pancreatic disease from patients with early- and late-stage histologically validated pancreatic cancer. Furthermore, they reported that levels of GPC1-positive circulating exosomes correlated with tumour burden and the survival of surgical patients. They concluded that GPC1-positive circulating exosomes is a promising non-invasive diagnostic and screening tool for the detection of early stage pancreatic cancer. Lu et al. Reference Lu, Niu, Liu, Gao, Sun and Zhao76 performed a comprehensive analysis of GPC1 mRNA and protein expression characteristics using RNA sequencing data from 178 PDAC patients from the cancer genome atlas (TCGA) and 186 subjects whose tissues were used in immunohistochemical staining assays. They demonstrated that GPC1 mRNA is absent in normal and adjacent non-cancerous pancreatic tissues but overexpressed in PDAC tissues and elevated levels is associated with poorer pathological differentiation and larger tumour size. They concluded that GPC1 is an independent unfavourable prognostic factor in PDAC and has the potential as an early diagnostic and prognostic marker as well as a promising therapeutic target for PDAC.
Macrophage Inhibitory Cytokine 1 (MIC-1)
Macrophage inhibitory cytokine 1 (MIC-1) is a member of the transforming growth factor β (TGF-β) superfamily cytokine Reference Wang, Li and Tian83–Reference Kunovsky, Tesarikova and Kala89 and it is implicated in the regulation of immune responses, adipose tissue function, cellular stress responses, body fat mass and tumour pathogenesis. Reference Bauskin, Brown and Kuffner88,Reference Agarwal, Hastak, Jackson, Breit, Stark and Agarwal90,Reference Lambert, Kelly and Shim91 Wang et al. Reference Wang, Li and Tian83 reported that MIC-1 plays a significant role in carcinogenesis related activities, such as proliferation, migration, apoptosis and angiogenesis in many types of solid tumours including PDAC. According to Chen et al., Reference Chen, Liu, Zhao, Wang, Gao and Chen87 MCI-1 has attracted attention as a biomarker because of its multifunctional roles in controlling numerous physiological and pathological processes. Several studies have reported that MIC-1 is negligibly expressed in most tissues under normal conditions, but is substantially overexpressed under pathological conditions such as injury, inflammation and in various cancers such as colon, prostate and pancreatic cancers. Reference Wang, Li and Tian83–Reference Koopmann, Rosenzweig and Zhang85,Reference Chen, Liu, Zhao, Wang, Gao and Chen87,Reference Kunovsky, Tesarikova and Kala89 According to Kaur et al., Reference Kaur, Baine and Guha86 MIC-1 is aberrantly expressed in pancreatic cancer tissues and Kunovsky et al. Reference Kunovsky, Tesarikova and Kala89 also reported elevated levels of serum MIC-1 in PDAC patients compared to patients with benign pancreatic diseases and healthy individuals. Chen et al. Reference Chen, Liu, Zhao, Wang, Gao and Chen87 and Kunovsky et al., Reference Kunovsky, Tesarikova and Kala89 have also reported that elevated levels of MIC-1 are associated with tumour progression and poor prognosis. Furthermore, Kunovsky et al. Reference Kunovsky, Tesarikova and Kala89 and Koopmann et al. Reference Koopmann, Rosenzweig and Zhang85 also reported that serum MIC-1 has a diagnostic accuracy comparable to CA 19-9 for PDAC and a combined serum MIC-1 and CA 19-9 measurements has superior diagnostic utility compared with CA 19-9 alone for differentiating patients with pancreatic cancer from healthy controls. According to Chen et al Reference Chen, Liu, Zhao, Wang, Gao and Chen87 and Bauskin et al, Reference Bauskin, Brown and Kuffner88 MCI-1 has the potential to play an important role in the diagnosis, prognosis and management of pancreatic cancer.
Kaur et al. Reference Kaur, Baine and Guha86 investigated the diagnostic potential of MIC-1 in 105 patients with symptoms suggestive of pancreatic diseases (i.e., patients with chronic pancreatitis, pancreatic cancer and non pancreatic non healthy patients) who underwent endoscopic pancreatic juice collection following secretin stimulation. They observed significantly elevated levels of MIC-1 in pancreatic juice of patients with pancreatic cancer and reported that MIC-1 has the potential to differentiate pancreatic cancer from chronic pancreatitis patients. Koopmann et al. Reference Koopmann, Rosenzweig and Zhang85 also compared the diagnostic utility of a panel of potential serum markers of pancreatic cancer using serum from 50 resectable pancreatic cancer patients, 50 chronic pancreatitis patients and 50 age and sex-matched healthy controls. They reported that both MIC-1 and CA 19-9 are significantly independent predictors of diagnosis however, MIC-1 is significantly better than CA19-9 in differentiating patients with pancreatic cancer from healthy controls. In a previous study, Koopmann et al. Reference Koopmann, Buckhaults and Brown84 evaluated 326 preoperative serum samples obtained from patients undergoing pancreaticoduodenectomy to investigate the diagnostic value of MIC-1 as a marker of pancreatic cancer. They reported significantly elevated serum MIC-1 levels in patients with PDAC than patients with benign pancreatic neoplasms, chronic pancreatitis or in healthy controls. Furthermore, they reported that elevated serum MIC-1 performed as well as CA 19–9 and the combination of MIC-1 and CA 19–9 significantly improved diagnostic accuracy and that serum MIC-1 measurement can aid in the diagnosis of pancreatic cancers. Wang et al. Reference Wang, Li and Tian83 investigated the diagnostic value of serum MIC-1 for early stage PDAC and its potential for monitoring treatment response using tumour tissue samples from 64 PDAC patients and serum from 1,472 PDAC, benign pancreas tumour and chronic pancreatitis patients and healthy controls. They reported significantly elevated levels of MIC-1 in PDAC tissues and serum samples, including those with negative CA 19·9 and early stage disease. Furthermore, they observed that serum MIC-1 has a better performance compared with CA 19·9 in discriminating early stage PDAC from control serum with higher sensitivity but similar specificity. Moreover, they also observed that serum MIC-1 level is significantly decreased in patients with PDAC after curative resection but returned to elevated levels when tumour relapse occurred. They concluded that serum MIC-1 may serve as a novel diagnostic marker in early diagnosis and post-operative monitoring of PDAC.
Human Equilibrative Nucleoside Transporter 1 (hENT1)
The human nucleoside transporters are known by their activity as transport systems and belong to the sodium-dependent, concentrative solute carrier 28 (SLC28) and the equilibrative, solute carrier 29 (SLC29) gene families. The SLC28 gene encodes the three human Concentrative Nucleoside Transporters (hCNT1, hCNT2, hCNT3) family, whereas the SLC29 gene encodes the four human Equilibrative Nucleoside Transporters (hENT1, hENT2, hENT3, hENT4) family. Reference Pérez-Torras, García-Manteiga and Mercadé92–Reference Bird, Elmasry and Jones95 According to Perez-Torras et al., Reference Pérez-Torras, García-Manteiga and Mercadé92 in vitro studies have shown that the uptake of most chemotherapeutic nucleoside analogues depends on the activity of these nucleoside transporters. The hENT1 protein is encoded by the SLC29A1 gene located on the short arm of chromosome 6 at position 21·1 (6p21·1) and mediates the transport of nucleotides (both purines and pyrimidines) into pancreatic cancer cells. Reference Pérez-Torras, García-Manteiga and Mercadé92,Reference Mohelnikova-Duchonova and Melichar94 Various studies have reported significantly elevated levels of the hENT1 protein in resected PDAC and as the major transporter responsible for gemcitabine uptake into human cells. Reference Pérez-Torras, García-Manteiga and Mercadé92–Reference Nordh, Ansari and Andersson99 According to Spratlin and Mackey, Reference Spratlin and Mackey97 hENT1 is capable of mediating gemcitabine uptake in the direction of the concentration gradient. Bird et al. Reference Bird, Elmasry and Jones95 reported that low or missing hENT1 expression levels in cellular membranes correlates with low levels of intracellular gemcitabine, whereas overexpression in pancreatic cancer cells increases the efficacy of gemcitabine treatment. Nordh et al. Reference Nordh, Ansari and Andersson99 and Perez-Torras et al., Reference Pérez-Torras, García-Manteiga and Mercadé92 also reported that high hENT1 expression is associated with alterations in nucleoside enzymatic machinery and cell cycle progression in cultured cells and enhances gemcitabine action in vivo. Furthermore, several studies have reported that high hENT1 protein expression levels in pancreatic cancer patients is correlated with significantly longer overall survival and disease-free survival in patients treated with gemcitabine and a potential predictor for gemcitabine efficacy in resected and advanced PDAC patients. Reference Pérez-Torras, García-Manteiga and Mercadé92–Reference Morinaga, Morinaga and Nakamura96,Reference Raffenne, Nicolle and Puleo98,Reference Greenhalf, Ghaneh and Neoptolemos100 According to Spratlin and Mackey, Reference Spratlin and Mackey97 evaluation of hENT1 has the strongest preclinical mechanistic support and the strongest clinical dataset to suggest an essential role as a predictive marker with which to guide treatment decisions.
Morinaga et al. Reference Morinaga, Morinaga and Nakamura96 retrospectively investigated the relationship between hENT1 expression levels and the outcome of resected pancreatic cancer followed by post-operative gemcitabine monotherapy in a cohort 27 resected patients treated with adjuvant gemcitabine. They observed that most of the patients expressed elevated levels of hENT1 and had a significantly longer disease-free and overall survival. They concluded that elevated hENT1 expression in pancreatic cancer is significantly associated with longer survival in patients treated with adjuvant gemcitabine monotherapy after curative resection, and that hENT1 immunohistochemistry is a significant and independent prognostic factor for survival. Greenhalf et al. Reference Greenhalf, Ghaneh and Neoptolemos100 also investigated the potential of tumour hENT1 levels to predict overall survival for patients treated with gemcitabine compared with patients receiving 5-fluorouracil (5FU) in an unbiased group of patients from two clinical trials. They reported that elevated hENT1 expression level is associated with a survival benefit for patients treated with gemcitabine compared with low hENT1 levels. They concluded that adjuvant gemcitabine should not be used after resection for patients with low tumour expression of hENT1, however, 5FU-based regimens can be used as the alternative. Furthermore, they reported that the assessment of hENT1 has a potential for stratified medicine approach in pancreatic cancer in both adjuvant and advanced settings. Farrell et al., Reference Farrell, Elsaleh and Garcia93 studied the predictive value of hENT1 expression levels in a cohort of 538 pancreatic adenocarcinoma patients recruited in a large prospective randomised adjuvant treatment trial (RTOG9704). Patients were randomly assigned to either gemcitabine or 5FU treatment after surgical resection. They reported that elevated hENT1 expression is correlated with overall and disease free survival in patients who received gemcitabine treatment, whereas elevated hENT1 expression is not associated with survival in patients treated with 5FU.
Interleukin-6 (IL-6)
Interleukin-6 (IL-6) is a pleiotropic cytokine implicated in various pathophysiological processes, including inflammation; haematopoiesis; immune regulation; tissue regeneration; cell proliferation, differentiation, survival and apoptosis; carcinogenesis and cancer progression, invasion, treatment resistance and prognosis. Reference Pop, Seicean, Lupan, Samasca and Burz101–Reference Goumas, Holmer and Egberts105 The IL-6 gene is located on the short arm of chromosome 7 at position 15·3 (7p15·3) and encodes the IL-6 protein. Reference Talar-Wojnarowska, Gasiorowska, Smolarz, Romanowicz-Makowska, Kulig and Malecka-Panas103 IL-6 is secreted by a broad variety of cells including macrophages, monocytes, endothelial cells, hepatocytes, fibroblasts and tumour cells and it is reported to mediates hepatocyte acute-phase protein synthesis and activates B, T and natural killer (NK) cells. Reference Mroczko, Groblewska, Gryko, Kędra and Szmitkowski104,Reference Błogowski, Deskur and Budkowska106 Although the role of IL-6 in cancer biology is still unclear, it is reported that increased serum IL-6 levels enhances the metastatic potential of cancer cells by upregulating the expression on endothelial cells receptors and by stimulating the growth factors, such as vascular endothelial growth factor (VEGF). Reference Pop, Seicean, Lupan, Samasca and Burz101,Reference Talar-Wojnarowska, Gasiorowska, Smolarz, Romanowicz-Makowska, Kulig and Malecka-Panas103,Reference Goumas, Holmer and Egberts105,Reference Błogowski, Deskur and Budkowska106 According to Pop et al., Reference Pop, Seicean, Lupan, Samasca and Burz101 IL-6 is involved in the regulation of physiological molecular pathways such as energy metabolism or increase of glucose production and in pancreatic cancer oncogenesis, metastases and treatment resistance. Several studies have reported that serum levels of IL-6 are normally undetectable in healthy controls, but are significantly elevated in patients with a variety of haematological and solid tumours including pancreatic, gastric, renal cell and ovarian cancers as well as after surgical procedures. Reference Pop, Seicean, Lupan, Samasca and Burz101,Reference Talar-Wojnarowska, Gasiorowska, Smolarz, Romanowicz-Makowska, Kulig and Malecka-Panas103,Reference Mroczko, Groblewska, Gryko, Kędra and Szmitkowski104,Reference Błogowski, Deskur and Budkowska106 According to Blogowski et al., Reference Błogowski, Deskur and Budkowska106 IL-6 promotes the formation of blood vessels within pancreatic cancer microenvironment, independently and/or synergistically influence the activity of immune cells, enhances the intensity of inflammatory processes and the invasiveness of pancreatic cells, therefore contributing to metastatic spread. According to Mroczko et al., Reference Mroczko, Groblewska, Gryko, Kędra and Szmitkowski104 serum levels of IL-6 are significantly higher in patients with pancreatic cancer than in patients with chronic pancreatitis and suggested that serum IL-6 is a potential negative prognostic factor for survival of pancreatic cancer patients. Various studies have shown that elevated levels of serum IL-6 is correlated with poor prognosis in patients with pancreatic adenocarcinoma. Reference Talar-Wojnarowska, Gasiorowska, Smolarz, Romanowicz-Makowska, Kulig and Malecka-Panas103–Reference Goumas, Holmer and Egberts105,Reference Miura, Mitsunaga and Shimizu107 Miura et al. Reference Miura, Mitsunaga and Shimizu107 observed that high serum IL-6 levels in advanced pancreatic cancer patients is associated with liver metastases, increased CEA, high C-reactive protein and low haemoglobin. However, according to Goumas et al., Reference Goumas, Holmer and Egberts105 the inhibition of IL-6 signalling is a potential therapeutic option for PDAC patients who could be treated with tocilizumab. Furthermore, preclinical murine studies have also indicated that targeted IL-6 inhibition can be combined with anti-programmed death ligand 1 therapy to potentially increase patient overall survival. Reference Mace, Shakya and Pitarresi108
Mroczko et al. Reference Mroczko, Groblewska, Gryko, Kędra and Szmitkowski104 investigated the diagnostic potential of pretreatment serological levels of IL-6 to differentiate between pancreatic cancer and chronic pancreatitis patients and its prognostic significance in a cohort of 78 pre-surgery pancreatic cancer patients, 45 chronic pancreatitis patients and 70 healthy controls. They observed significantly elevated pre-surgery serum levels of IL-6 in cancer patients than in healthy controls. Furthermore, they reported significantly elevated IL-6 levels in non-resectable tumours, tissues of resected pancreatic cancer patients, patients who died during a 2-year observation period and in more advanced tumours and correlated with increased tumour size, presence of nodal involvement and distant metastases. They concluded that serum IL-6 is a significant prognostic factor of patients’ survival and suggested the use of serum IL-6 in the diagnosis and prognosis of patients with pancreatic cancer and in the differentiation from chronic pancreatitis patients. Talar-Wojnarowska et al. Reference Talar-Wojnarowska, Gasiorowska, Smolarz, Romanowicz-Makowska, Kulig and Malecka-Panas103 also assessed the clinical significance of IL-6 serum level in patients with pancreatic cancer and chronic pancreatitis in 41 pancreatic adenocarcinoma patients, 56 chronic pancreatitis patients and 50 sex- and age-matched healthy controls. They reported significantly elevated IL-6 serum levels in pancreatic adenocarcinoma and chronic pancreatitis patients than in healthy controls and the elevated levels correlated with tumour size and the presence of liver metastases. They concluded that elevated serum levels of IL-6 in patients with pancreatic adenocarcinoma (especially patients with larger tumour size and the presence of liver metastases) could potentially discriminate patients with extremely poor prognosis. Zhang et al. Reference Zhang, Yan and Collins109 studied whether IL-6 expression is required for the initiation, maintenance and progression of pancreatitis-associated pancreatic cancer using genetically engineered mouse models of pancreatic cancer. They reported that IL-6 expression is important for the onset of pancreatic intraepithelial neoplasia and thus pancreatic cancer initiation and plays a role in pancreatic cancer maintenance and progression. They concluded that IL-6 plays a major role at all stages of pancreatic carcinogenesis and using anti-IL-6 antibody is a potential therapeutic option for pancreatic cancer patients. Goumas et al. Reference Goumas, Holmer and Egberts105 accessed the treatment efficacy of tocilizumab (a human monoclonal anti-IL-6R antibody) on cancer growth in orthotopic xenografts of human pancreatic cancer cell lines in a mouse model. They reported that treatment with tocilizumab significantly reduces tumour growth in the mice model and after surgical resection of the primary tumour decreased the local recurrence rate and reduced the number of distant metastases. They concluded that using IL-6 inhibitors is a potential new treatment option for PDAC and an option to reduce systemic inflammation, reduce tumour recurrence and metastasis and potentially improve the quality of life of pancreatic cancer patients.
Conclusion
The poor prognosis of pancreatic cancers is mainly due to the difficulty of detection at an early stage and in addition, the early detection of the disease without the use of invasive methods has been challenging. Thus, advancement in pancreatic cancer management towards the concept of precision medicine that account for individual patient variabilities will require the identification of effective clinical biomarkers capable of therapeutic targeting of specific genetically aberrant pathways, which play key roles in malignant tumour formation as well as offer improved understanding of the biology responsible for pancreatic carcinogenesis and progression. Emerging pancreatic biomarkers are capable of early diagnosis of the disease in symptomatic patients before the onset of metastasis to improve resectability and early detection of the disease in asymptomatic individuals at high risk for developing the disease as well as development of new and more effective therapies for improved treatment outcome and patients’ survival. Consequently, the use of cost-effective, accurate biomarkers or panel of biomarkers with high specificity and sensitivity that has the potential to account for individual patient variabilities to facilitate rapid and early disease diagnosis, screen high-risk populations, improve treatment outcome and patients’ survival as well as patient monitoring during treatment will likely shift the treatment paradigm of pancreatic cancer towards a more personalised and targeted medicine. Personalised medicine has the potential for patient-specific intervention based on patient-specific disease susceptibility, diagnostic or prognostic information or treatment selection for the optimum response thereby substantially impacting disease mortality and potentially increase patient survival.
Acknowledgement
N/A.
Conflict of Interest
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
