Dna Mismatch Repair Deficiency And Benefit From Adjuvant Bevacizumab In Nsabp C-08: Molecular Profiling Results

55 Background: The purpose of this study was to identify biomarkers that define a subset of patients who received benefit from bevacizumab (bev) in NSABP trial C-08, even though bev did not improve outcomes over standard adjuvant chemotherapy (CT) in the treatment of stage II and III colon cancer.A randomly selected cohort of C-08 cases (N=500) were profiled for whole genome expression (N=445) and for mutations (N=463) in KRAS, NRAS, PIK3CA, and MET. BRAF mutations and mismatch repair (MMR) status were profiled on the available cases (N=1,764 and 1,993, respectively). Cox proportional hazard models were used to assess prognosis and prediction for the value of bev using overall survival (0S) and time to recurrence (TTR) as end points.The effect of bev was different for MMR deficient (MMR-d) and proficient tumors for OS (interaction p=.035) but not TTR (interaction p=.08). Patients with MMR-d (N=252) tumors showed a significant benefit from the addition of bev to CT for OS (hazard ratio =0.52 (95% CI: 0.29-0.94, p=0.028). KRAS, NRAS, PIK3CA, and MET were not significant for interaction with bev in the discovery cohort. BRAF mutations were associated with MMR status (p<.0001) and the prognostic value of MMR depended on BRAF for TTR (interaction p=.027) but not OS (interaction p=.31). The effect of bev was independent of BRAF (interaction p=.28 TTR and .37 OS). Three-factor interaction tests for bev, MMR, and BRAF were not significant for either endpoint. Gene expression analysis with BRB array tools identified 5 BioCarta pathways (p<0.05) which differentially expressed in 4 statistical tests; 4 of these pathways were directly or indirectly involved in T cell activation and one was involved in the activation of VEGF.Patients in C-08 with MMR-d tumors received benefit from bev treatment but these results need to be validated in a separate study. Gene expression data suggest that T-cells may be differentially expressed based on MMR status. Activation of VEGF has been shown to suppress T-cell development (Ohm et al. Blood. 2003:10;4878). A speculative possibility for the benefit of bev in MMR-d tumors may be due to blocking of VEGF, releasing T cells from VEGF suppression.