Pharmacogenetic analysis in metastatic colorectal cancer (mCRC) patients (pts) treated with second-line irinotecan (IR)+/− cetuximab (CB): The EPIC experience
4022 Background: EPIC, a multinational phase III clinical trial with IR + CB vs IR alone in mCRC pts 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 pts treated with CB/IR vs. IR alone. Methods: DNA was extracted from all available formalin-fixed paraffin-embedded tumor samples from the phase III EPIC trial (US sites only). Genotyping was performed using PCR-RFLP assays and 5’ -end [g-33P] ATP’ labeled PCR-protocols. Results: 186 pts were treated either with IR/CB (arm A, 84 pts) or IR (arm B, 102 pts) only. In arm A, 11/84 pts (13%) showed CR or PR, whereas 73/84 (87%) pts had SD or PD. For arm B, 6/102 pts (6%) showed CR or PR, whereas 96/102 pts (94%) had SD or PD. Median PFS in arm A was 3.0 months (95%CI: 2.4- 4.1 months) vs 2.7 months (95%CI: 2.2–2.9 months) in arm B; median overall survival (OS) was 9.3 months (95%CI: 7.1–12.1 months) in arm A vs. 12.3 months (95%CI: 10.4- 17.9 months) in arm B. K-ras mutation status was not significantly associated with PFS or response to CB/IR in the subgroup 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). In arm B, we found a significant association with RR (p=0.0103, Fisher's exact test) for MTHFR1298. Furthermore, MTHFR 677 (p =0.0048, log-rank test) and MTHFR 1298 (p=0.038, 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 677 and MTHFR 1298 was associated with OS (adjusted p=0.028 and 0.026, respectively, Cox-proportional hazards models), independent from K-ras mutation status, race and number of disease sites. Conclusions: Our study demonstrates the potential predictive value of polymorphisms in the EGFR- and MTHFR- gene in mCRC pts treated with IR+ CB. Further validation in additional clinical trials is necessary. [Table: see text]