Prognostic Impact of IL6 Genetic Variants in Patients with Metastatic Colorectal Cancer Treated with Bevacizumab-Based Chemotherapy.

PURPOSE The IL6/STAT3 axis promotes inflammation, angiogenesis, and cancer. The effect of genetic variants within this pathway on benefit from antiangiogenic cancer therapy is unknown. We tested whether SNPs in genes involved in IL6/STAT3 signaling can predict efficacy of bevacizumab-based chemotherapy in metastatic colorectal cancer (mCRC) patients. EXPERIMENTAL DESIGN Associations between potentially functional IL6 (rs2069837 and rs1800795) and STAT3 (rs744166 and rs4796793) SNPs and clinical outcomes [progression-free survival (PFS), overall survival, and tumor response rate] were evaluated in mCRC patients receiving first-line FOLFIRI plus bevacizumab in two randomized phase III trials: TRIBE (n = 223, training cohort) and FIRE-3 (n = 288, validation cohort). Patients receiving FOLFIRI plus cetuximab in FIRE-3 (n = 264) served as a control cohort. The interaction between genotype and primary tumor location with clinical outcomes was examined. Genomic DNA isolated from whole blood or tumor tissue was analyzed by PCR-based direct sequencing. RESULTS Patients with an IL6 rs2069837 G allele treated with FOLFIRI plus bevacizumab had an inferior PFS than those with the A/A genotype in TRIBE [9.4 vs. 11.1 months; HR = 1.53; 95% confidence interval (CI), 1.12-2.10; P = 0.004] and FIRE-3 (8.8 vs. 10.9 months; HR = 1.40; 95% CI, 1.06-1.85; P = 0.015). These associations were confirmed in multivariable analyses and were not seen in the control cohort. In subgroup analysis, the effect of IL6 rs2069837 on PFS was present only in patients with left-sided cancers, but the test for interaction was not significant. CONCLUSIONS IL6 rs2069837 genotype is a clinically relevant prognostic factor in mCRC patients treated with first-line bevacizumab-based chemotherapy. Clin Cancer Res; 22(13); 3218-26. ©2016 AACR.