FcγRIIa and FcγRIIIa Polymorphisms and Cetuximab Benefit in the Microscopic Disease

Purpose: Fc gamma R polymorphisms have been reported to enhance the immune-mediated effects of cetuximab in metastatic colorectal cancer. There are no data on the relationship between these polymorphisms and cetuximab in the early-stage setting. We performed a pharmacogenomic analysis of EXPERT-C, a randomized phase II trial of neoadjuvant CAPOX followed by chemoradiotherapy, surgery, and adjuvant CAPOX +/- cetuximab in high-risk, locally advanced rectal cancer. Experimental Design: Fc gamma RIIa-H131R and Fc gamma RIIIa-V158F polymorphisms were analyzed on DNA from peripheral blood samples. Kaplan-Meier method and Cox regression analysis were used to calculate survival estimates and compare treatment arms. Results: Genotyping was successfully performed in 105 of 164 (64%) patients (CAPOX = 54, CAPOX-C = 51). No deviation fromthe Hardy-Weinberg equilibrium or association of these polymorphisms with tumor RAS status was observed. Fc gamma RIIa-131R (HR, 0.38; P = 0.058) and Fc gamma RIIIa-158F alleles (HR, 0.21; P = 0.007) predicted improved progression-free survival (PFS) in patients treated with cetuximab. In the CAPOX-C arm, carriers of both 131R and 158F alleles had a statistically significant improvement in PFS (5 years: 78.4%; HR, 0.22; P = 0.002) and overall survival (OS; 5 years: 86.4%; HR, 0.24; P = 0.018) when compared with patients homozygous for 131H and/or 158V (5-year PFS: 35.7%; 5-year OS: 57.1%). An interaction between cetuximab benefit and 131R and 158F alleles was found for PFS (P = 0.017) and remained significant after adjusting for prognostic variables (P = 0.003). Conclusion: This is the first study investigating Fc gamma RIIa and Fc gamma RIIIa polymorphisms in patients with early-stage colorectal cancer treated with cetuximab. We showed an increased clinical benefit from cetuximab in the presence of 131R and 158F alleles. (C) 2014 AACR.