Worse prognosis of KRAS C.35 G > A mutant metastatic colorectal cancer (MCRC) patients treated with intensive triplet chemotherapy plus bevacizumab (FIr-B/FOx)

521 Background: Bevacizumab (BEV) addition to doublet chemotherapy significantly increases efficacy without differentially affecting prognosis in KRAS wild-type (wt) and mutant (m) MCRC. Present study evaluates clinical outcome of BEV added to triplet chemotherapy, FIr-B/FOx (Bruera G et al, BMC Cancer 2010, 10:567), according to KRAS genotype. Methods: MCRC patients (pts) were treated with first line FIr-B/FOx regimen including BEV (5 mg/kg, days 1,15) and triplet chemotherapy, weekly alternating irinotecan (160 mg/m2 days 1,15) or oxaliplatin (80 mg/m2, days 8, 22) associated to fluorouracil (900 mg/m2, days 1-2, 8-9, 15-16, 22-23); every 4 weeks. Tumoral samples were simultaneously screened for KRAS codon 12 and 13, and BRAF c.1799 T > A mutations by SNaPshot multiplex assay (Di Fiore F, Br J Cancer 2007;96(8):1166-1169) and/or direct sequencing. Activity and efficacy were evaluated and compared using log-rank test. Results: Forty-five MCRC pts were evaluated: 25 KRAS wt (56%), 20 KRAS m (44%). After 30 months median follow-up, objective response rate (ORR), progression-free survival (PFS) and overall survival (OS) were, respectively: KRAS wt 88% (C.I. ± 14), 14 months, 38 months; KRAS m 80% (C.I. ± 19), 12 months, 21 months. PFS and OS were not significantly different. Among KRAS m pts, ORR, PFS and OS at 19 months median follow-up in c.35 G > A (13 pts) were 69% (C.I. ± 26), 9 months, 11 months, respectively. OS of c.35 G > A KRAS m was significantly worse compared to KRAS wt (p = 0.003) and to other than c.35 G > A mutant pts (p = 0.022). Conclusions: First line FIr-B/FOx intensive regimen adding BEV to triplet chemotherapy can further increase activity and efficacy without significantly affecting different clinical outcome in KRAS wt and m MCRC pts. A significant interaction between the most prevalent c.35 G > A KRAS mutation and worse prognosis was observed, compared to KRAS wt pts and to other than c.35 G > A KRAS exon 2 mutations, depending from different biological aggressiveness and sensitivity to BEV addition to triplet chemotherapy.