Polymorphisms in Cyclooxygenase-2 and Epidermal Growth Factor Receptor Are Associated with Progression-Free Survival Independent of K-ras in Metastatic Colorectal Cancer Patients Treated with Single-Agent Cetuximab

Purpose: Recently, an objective response rate of 12% was reported in a phase II study of cetuximab in patients with epidermal growth factor receptor (EGFR)-expressing metastatic colorectal cancer (mCRC) refractory to fluoropyrimidine-, oxaliplatin-, and irinotecan-based chemotherapy (IMC-0144). In this large molecular correlates study, we tested whether K-ras mutation status and polymorphisms in genes involved in the EGFR-signaling pathway were associated with clinical outcome in IMC-0144. Experimental Design: We analyzed all available tissue samples from 130 of 346 mCRC patients enrolled in the IMC-0144 phase II clinical trial of cetuximab. Genomic DNA was extracted from formalin-fixed paraffin-embedded tumor tissues, and K-ras mutation status and the genotypes were analyzed using PCR-RFLP, direct DNA-sequencing, and 5′-end [γ-33P] ATP–labeled PCR-protocols. Results: The PFS of patients with cyclooxygenase-2 (COX-2) −765 G>C [C/C; risk ratio (RR), 0.31; 95% confidence interval (95% CI), 0.12-0.84; P = 0.032], COX-2 +8473 T>C (C/C; RR, 0.67; 95% CI, 0.40-1.13; P = 0.003), EGF +61 A>G (G/G; RR, 0.57; 95% CI, 0.34-0.95; P = 0.042), and EGFR +497 G>A (A/G; RR, 0.82; 95% CI, 0.56-1.20; P = 0.017) genotypes was significantly longer compared with those with other genotypes. In addition, patients whose tumors did not have K-ras mutations showed better RR, PFS, and overall survival than patients with K-ras mutations. In multivariable analysis, COX-2 +8473 T>C (adjusted P = 0.013) and EGFR +497 G>A (adjusted P = 0.010) remained significantly associated with progression-free survival, independent of skin rash toxicity, K-ras mutation status, and Eastern Cooperative Group performance status. Conclusions: Polymorphisms in COX-2 and EGFR may be useful independent molecular markers to predict clinical outcome in patients with mCRC treated with single-agent cetuximab, independent of skin rash toxicity, K-ras mutation, and Eastern Cooperative Oncology Group performance status.