Biomarkers and Pharmacogenetics in Pancreatic Cancer

Author Title Stage of cancers Main findings #4022 McWilliams, et al. [3] Genome-wide interaction study of gemcitabine treatment and genotype on survival in pancreatic cancer All stages Nine out of 550,000 SNPs found as potential predictive biomarkers for gemcitabine therapy. No SNPs-specific toxicities are noticed #e14657 de Albuquerque, et al. [9] Prognostic significance of multimarker circulating tumor cell analysis in patients with advanced pancreatic cancer Advanced pancreatic cancer Presence of circulating tumors cells detected by multiantibody enriched techniques is an independent prognostic marker for progression free survival #e14645 Ueno, et al. [13] Effect of cytidine deaminase (CDA)-related biomarkers on overall survival in patients with advanced pancreatic cancer receiving gemcitabine monotherapy Advanced pancreatic cancer Reduced CDA activity correlated well with prolonged survival of advanced pancreatic cancers patients. CDA*3 is a one of the factors that reduced CDA activity in Japanese patients. #4047 Boeck, et al. [16] Molecular markers of the EGFR pathway in erlotinibtreated patients with advanced pancreatic cancer: Translational analyses of a randomized cross-over AIO phase III trial Advanced pancreatic cancer Molecular markers of the EGFR pathway were tested but only mutation of K-ras at exon 2 might be associated with treatment outcome in erlotinib-treated patients with APC. Figure 1. Circulating tumor cells and process of metastasis (Copyright ©2002 from Molecular Biology of the Cell by Alberts et al. [18]. Reproduced by permission of Garland Science/Taylor & Francis LLC). JOP. J Pancreas (Online) 2011 Jul 8; 12(4):325-329. JOP. Journal of the Pancreas http://www.joplink.net Vol. 12 No. 4 July 2011. [ISSN 1590-8577] 327 but carries higher toxicities [2]. As such, it is desirable to identify those patients who will benefit the most from traditional gemcitabine-based therapy to minimize unnecessary toxicities-associated morbidities. McWilliams et al. (Abstract #4022 [3]) was able to present a study identifying 9 SNPs as good predictive markers for gemcitabine therapy, by using a genome-wide interaction study on a large cohort of 940 patients. In their study, initial 550,000 SNPs from 413 patients of all stages of pancreatic cancer treated with gemcitabine were screened for treatment-benefit interaction with overall survival being the endpoint. The 100 most significant SNPs from initial stage were further analyzed on another 527 patients for concordant effects from gemcitabine therapy. The authors were able to identify a total of nine such SNPs that have statistically significant favorable predictive power in gemcitabine efficacy. Specifically, genes PYCARD (rs6507115) and MAPRE2 (rs8056505) were strongly correlated with gemcitabine efficacy in both stages, which makes them potential genomic predictive biomarkers. No SNPs has been found to have significant association with gemcitabine toxicities. Circulating Tumor Cells (CTCs) Circulating tumor cells (CTCs) are cancer cells that are detached from primary tumor sites and travel in the peripheral blood circulation system, leading to distant metastasis [4] (Figure 1). CTCs are typically enriched and detected via immunomagnetic separation system [5] or via microfluidic CTC-chip system [6, 7]. Both adenocarcinoma [6] and neuroendocrine [8] pancreatic CTCs have been detected. Khan et al., had shown original preliminary results suggesting the prognostic and predictive values of CTCs in neuroendocrine pancreatic cancer [8]. De Albuquerque et al. (Abstract #e14657 [9]) reported the prognostic values of CTCs detection in pancreatic adenocarcinoma. By using the high affinity antibodies BM7 (MUC 1) in addition to conventional VU1D9 (EpCAM), CTCs detection were reported in 49.3% of 144 peripheral blood samples from 39 patients with advanced pancreatic adenocarcinoma. The detection of such CTCs portended poor prognosis (median progression free survival: 60.7 days vs. 163.6 days in patients with positive CTCs detection and negative CTC detections, respectively; P<0.0001). As such, authors concluded that CTCs can act as an independent prognostic biomarker. Cytidine Deaminase (CDA) and CDA*3 Cytidine deaminase (CDA) genotype and phenotype as negative predictive markers for gemcitabine was further elucidated. Gemcitabine is deactivated by CDA to an inactive form, 2’,2’-difluorodeoxyuridine (dFdU), during its biotransformation [10] (Figure 2). CDArelated biomarkers predicting gemcitabine-induced toxicities, as well as negative efficacy, have been previously reported [11]. Conversely, it has also been reported that homozygous CDA*3, a non-synonymous SNPs of CDA (208 G>A) is associated with very low plasma CDA level and, thus, largely induces high level of gemcitabine and its associated toxicities [12]. Ueno et al. (Abstract #e14645) reported their results of CDA-related phenotypic and genetic biomarkers on the overall survival of advanced pancreatic cancer patients treated with gemcitabine monotherapy [13]. Markers including mean residence time of gemcitabine, plasma concentration of dFdU at 0.5 h (C0.5), plasma CDA activity, as well as CDA*2 and CDA*3 genotype, were studied. Results from two studies were reported. During their first study (n=73), univariate analysis was applied between biomarkers and overall survival. Significant survival advantage was found in patients who have longer mean residence time and higher C0.5 (P=0.0138 and P=0.0011, respectively). Accordingly, low plasma CDA activity and heterozygous CDA*3 were also significantly associated with prolonged overall survival (P=0.0062 and P=0.0247, respectively). In a second study (n=98), where multivariate Cox proportional hazard model was used, low plasma CDA level was again confirmed to be associated with longer overall survival and positive trend between CDA*3 heterozygosity and overall survival was observed though statistical significance was not achieved (Table 2). No statistically significant associations between CDA*2 and survival benefits were observed in either studies. Molecular Markers of the EGFR Pathway in ErlotinibTreated Patients with Advanced Pancreatic Cancer Gemcitabine plus erlotinib, EGFR tyrosine kinase inhibitor, has been approved by U.S. Food and Drug Administration as a first line therapy for patients with Figure 2. Gemcitabine biotransformation (adapted from Gilbert et al. [10]). DCK: deoxycytidine kinase; dFdC: gemcitabine; dFdCDP: gemcitabine diphosphate; dFdCMP: gemcitabine monophosphate; dFdCTP: gemcitabine triphosphate; dFdU: 2′,2′-difluorodeoxyuridine; dFdUMP: 2′,2′-difluorodeoxyuridine monophosphate; UMPCMPK: deoxycytidylate kinase. JOP. J Pancreas (Online) 2011 Jul 8; 12(4):325-329. JOP. Journal of the Pancreas http://www.joplink.net Vol. 12 No. 4 July 2011. [ISSN 1590-8577] 328 locally advanced or metastatic pancreatic cancer as statistically significant overall survival and progresssion-free survival have been reported in a phase III double-blind trials (n=569) [14]. To further assess if potential molecular biomarkers in the EGFR pathway can be identified, retrospective analysis was performed on the Arbeitsgemeinschaft Internistische Onkologie (AIO) phase III trial [15] where similar overall survival was ascertained between patients with advanced pancreatic cancer receiving either capecitabine plus erlotinib followed by gemcitabine monotherapy or gemcitabine plus erlotinib followed by capecitabine monotherapy. The authors (Abstract #4047 [16]) performed tissue analysis on the archived formalin fixed paraffin embedded tumor tissues on 208 patients. The followings markers were included in the analysis: Kras exon 2 mutation status, EGFR expression, PTEN expression, EGFR intron 1 polymorphism, and EGFR exon 13 R497K polymorphism. About 70% of patients are found to have K-ras mutations while 96% showed EGFR expression by immunohistochemistry. In univariate biomarker analyses, only K-ras mutations status was found to have significant associations with overall survival benefit (hazard ratio: 1.68; 95% CI: 1.17-2.41; P=0.005). Additionally, none of the aforementioned biomarkers were found to have statistically significant association with skin rashes, a common side effect from erlotinib. Therefore, definitive translation data is still relatively limited from this study, though authors have proven the feasibility to perform retrospective biomarker analysis on archived tissues data from this AIO phase III trial.