Predictive biomarkers of response to cetuximab in Chinese patients with metastatic colorectal cancer.

Abstract

e14085 Background: The paraffin-embedded tumor samples of 183 Chinese patients (pts) with metastatic colorectal cancer (mCRC) who had chemotherapy (chemo) over a period of 3.3 years were analyzed for the presence of KRAS, PIK3CA and BRAF mutations. Methods: PCR-direct sequencing was performed in micro-dissected tumor cells. The relationship between mutation and survival was evaluated using the Proportional Hazard Model, and relationship with drug response was evaluated with logistic regression. Multivariate analysis was used to adjust for the influence of age, sex, prior lines of chemo, use of bevacizumab (Bev) and the number of sites of metastases. Results: The median age was 58 yrs, over 50% of pts had > 2 lines of chemo and 50% had cetuximab. The prevalence of KRAS, BRAF and PI3KCA mutations were: 55%, 5%, 20% respectively. The prevalence of each KRAS mutation subtype was: G12D (36%), G12V (22%) and G13D (16%). KRAS mutation and prior use of Bev were independent prognostic factors with respective hazard ratios (HR) of 1.5 (95% CI = 1.05-2.16, p = 0.03) and 0.51 (95% CI = 0.3-0.87, p = 0.01). In the subgroup of patients who received cetuximab and chemotherapy in the first-line setting, KRAS mutation was associated with a lack of response to chemo with odd ratio (OR) of 0.1 (95% CI = 0.01-0.79, p=0.03). There was no correlation between the presence of BRAF and/ or PIK3CA mutations and OS or drug response. Five pts had co-expression of KRAS and PIK3CA mutations and none of them responded to cetuximab. Of the 14 pts who had complete response or prolonged disease stabilization to cetuximab-chemo, 4 had KRAS mutation, 1 had PIK3CA mutation and none had BRAF mutations. Conclusions: The prevalence of KRAS, BRAF and PIK3CA mutations reported in this Chinese cohort is consistent with reports from other non-Asian populations. KRAS mutation is an independent negative prognostic factor in chemo-treated pts with mCRC. KRAS mutation was associated with poorer response to 1st line cetuximab-based chemo.