Prospective evaluation of cetuximab-mediated antibody-dependent cell cytotoxicity in metastatic colorectal cancer patients predicts treatment efficacy

Cetuximab is a monoclonal antibody to the EGFR that induces antibody-dependent cell cytotoxicity (ADCC) through Fcg receptors on immune cells. Although SNPs in genes encoding Fcg receptors are functionally relevant to cetuximab-mediated ADCC in colorectal cancer, a direct correlation between in vitro ADCC and clinical response to cetuximab is not defined. We therefore enrolled 96 consecutive metastatic colorectal cancer (mCRC) patients at diagnosis in a study that assessed FcγR status and cetuximab-mediated ADCC. Patients carrying the FcγRIIa H alleles 131H/H and 131H/R had significantly higher ADCC compared with patients with the 131R/R alleles (P = 0.013). Patients carrying FcγRIIIa genotypes with the V alleles 158V/V and 158V/F displayed higher ADCC compared with patients carrying the 158F/F genotype (P = 0.001). Progression-free survival of patients with an FcγRIIIa 158V allele was significantly longer compared with patients carrying 158F/F (P = 0.05), whereas no significant difference was observed for overall survival. Twentyeight of 50 mCRC patients with wild-type KRAS received cetuximab. The average ADCC-mediated killing was 30% of assay targets for patients who experienced cetuximab complete or partial response, 21% in patients with stable disease and 9% in patients with progressive disease. To characterize basal natural killer (NK) activity, cytotoxicity was evaluated in 39 of 96 mCRC patients. Patients who responded to first-line treatment had higher NK-cell cytotoxicity. Thus, although limited to this cohort of patients, in vitro cetuximab-mediated ADCC correlated with FcgR polymorphisms and predicted cetuximab responsiveness.