The Association of FCGR2A and FCGR3A polymorphisms with outcomes in cetuximab treated metastatic colorectal cancer patients: CCTG and AGITG CO.20 trial analysis.

633 Background: We previously reported that the Fc-gamma receptor (FCGR) germline polymorphism in the FCGR2A gene (rs1801274; His (H) to Arg (R) substitution) but not FCGR3A (rs396991; Phe (F) to Val (V)) was associated with cetuximab benefit on overall survival (OS) in metastatic colorectal cancer patients (CCTG CO.17 trial). We performed a validation of these results in CO.20, a randomized trial of cetuximab+placebo vs. cetuximab+brivanib for metastatic, chemotherapy refractory, wild type K-RAS colorectal cancer. Methods: After genotyping DNA extracted from whole blood, the polymorphism relationships with OS and progression-free survival (PFS) were assessed using log-rank tests and hazard ratios (HR) from Cox proportional hazard models, adjusting for known prognostic factors. Results: Of 592/725 (82%) K-RAS wild type patients with available DNA and genotyping, those carrying the higher affinity FCGR2A H/H genotype (N = 165; 28%) had improved OS (HR 0.53; 95%CI:0.41-0.68) and PFS (HR 0.65; 95%CI:0.51-0.83) compared to those carrying the lower affinity R/R genotype (N = 128; 22%), corresponding to median absolute benefits of 3.7 (OS) and 3.3 months (PFS). The H/R genotype (N = 299; 50%) had intermediate outcomes. No significant associations were found between FCGR3A genotype and OS or PFS. No interaction between FCGR polymorphisms and treatment arm was observed. Patients carrying the double wild type combination of FCGR2A H/H and FCGR3A F/F genotypes (N = 45; 7.6%) had significantly better outcomes than other patients, particularly those carrying the rare (N = 11; 2%) R/R+ V/V genotype combination, corresponding to median absolute benefits of 12.5 (OS; HR 0.33 95%CI:0.16-0.68) and 4.5 (PFS; HR 0.45 95%CI:0.22-0.92) months. There were no significant associations between FCGR polymorphisms and either any grade of 3/4 toxicity or skin rash. Conclusions: In KRAS-wild type, cetuximab-treated patients, FCGR2A polymorphism was independently replicated to be associated with clinical outcome without affecting toxicity profiles. Additionally, in this large dataset, FCGR3A appears to modulate the relationship between FCGR2A polymorphism and outcome.