Pharmacogenetic analysis in metastatic colorectal cancer (mCRC) patients treated with second-line irinotecan (IR)+/- cetuximab (CB): The EPIC experience Dongyun Yang 1, Alexandra Pohl 1, Wu Zhang 1, Georg Lurje 1, Yan Ning 1, Anthony El-Khoueiry 1, Shirin Khambata-Ford 2, Christiane Langer 2, Syma Iqbal 1 and Heinz-Josef Lenz 1 1.USC/Norris Comprehensive Cancer Center, Los Angeles, CA 2. Bristol Myers Squibb Research and Development, Princeton, NJ Introduction Patients and method Results Conclusion Our study demonstrates a prognostic and potentially predictive value for polymorphisms in the EGFR- and MTHFR- gene in patients with mCRC, treated in second-line setting with IR+/- CB. To our knowledge, this is the first study to show a potential influence of MTHFR with irinotecan-sensibility. However, the underlying molecular mechanisms are unclear and need further in vivo- and in vitro evaluation. Genomic DNA was extracted from formalin- fixed paraffin-embedded tumor samples from 186 EPIC- trial participants (US sites only, 14% of total trial participants). 84 patients were treated with IR/CB (arm A); 102 patients received IR alone (arm B). Genotyping was performed using PCR-RFLP assays, direct sequencing or 5’ -end [ ϒ - 33 P] ATP’ labeled PCR-protocols. EPIC, a multinational phase III clinical trial with IR + CB vs IR alone in mCRC patients in the second-line setting after failure of FOLFOX demonstrated a benefit for IR+CB in progression-free survival (PFS) and response rate (RR). We evaluated functional germline polymorphisms involved in the EGFR- (EGF, EGFR), angiogenesis- (VEGF, IL-8, CXCR-2) - and drug-metabolism related genes (UGT1A1, MTHFR) for their potential role as molecular predictors for clinical outcome in patients treated with CB/IR vs. IR alone. In this patient cohort, 11/84 patients (13%), who received IR/CB, showed CR or PR, whereas 73/84 (87%) patients had SD or PD. For arm B, 6/102 patients (6%) showed CR or PR, whereas 96/102 patients (94%) had SD or PD. Median PFS in arm A was 3.0 months (range months) vs 2.7 months (range months) in arm B; median overall survival (OS) was 9.3 months (range months) in arm A vs months (range months) in arm B. Patients baseline characteristics were not representative for the whole study population (table 1). K-ras mutation status was not significantly associated with PFS or response to CB/IR in this patient cohort of 186 patients. We found an EGFR-CA- repeat in intron 1 in arm A to be associated with PFS (p=0.031, log- rank test), whereas the EGFR-CA repeat in arm B was not significantly associated with PFS (p=0.98, log-rank test). In arm B, we found a significant association with RR (p=0.0103, Fisher’s exact test) for MTHFR 1298A>C. Furthermore, MTHFR 677C>T (p =0.005, log-rank test) and MTHFR 1298A>C (p=0.039, log-rank test) were also found to be associated with OS in arm B. In multivariate analysis, EGFR-CA-repeat was significantly associated with PFS (adjusted p= 0.023). Furthermore, MTHFR 677C>T and MTHFR 1298A>C appeared to be prognostic factors for OS (adjusted p=0.028 and 0.026, respectively, cox-proportional hazard models), independent from K-ras mutation status, race and number of disease sites. OS by MTHFR 677C>T for arm B OS by MTHFR 1298A>C for arm B PFS by EGFR-CA repeat for arm A Patients baseline characteristics