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

Abstract

e14596 Background: Prognosis of MCRC patients (pts) treated with bevacizumab (BEV) and chemotherapy (CT) is not significantly different according to KRAS genotype. Specificmutations confer different aggressiveness. Prognostic relevance of the prevalent c.35 G > A KRAS mutation was retrospectively evaluated in pts treated with first line FIr-B/FOx, and post-progression. Methods: KRAS codon 12/13 and BRAF mutations were screened by SNaPshot and/or sequencing. FIr-B/FOx: weekly 2 days/12h-timed-flat-infusion/5-fluorouracil 900 mg/m2, weekly alternating irinotecan 160 mg/m2/BEV 5 mg/kg, or oxaliplatin 80 mg/m2. Second-line treatment was selected according to fitness, KRAS genotype, previous efficacy and safety. Efficacy was evaluated and compared according to treatment or KRAS genotype, using log-rank. Results: At 21.5 months, 59 pts were evaluated. KRAS mutant pts: c.35 G > A, 15 (25.4%); c.35 G > T, 7 (11.8%); c.38 G > A, 3 (5%); other, 3 (5%). KRAS wild-type, 31 pts (52.7%). ORR, PFS, OS were, respectively: c.35 G > A, 71%, 9 months, 14 months; other mutants, 61%, 12 months, 39 months. OS was significantly worse in c.35 G > A pts compared to KRAS wild-type (p = 0.002), KRAS/BRAFwild-type (p = 0.03), other pts (p = 0.002), other mutants (p = 0.05), other codon 12 (p = 0.03) mutant pts; PFS was not significantly different. Post-progression, at 14 months follow-up, PFS and OS were significantly worse in c.35 G > A compared to wild-type and/or other mutant pts. ORR of second line treatments was 38%, metastasectomies 12.5%, PFS 10 months, OS 14 months. PFS and OS were significantly favourable in pts treated with triplet CT plus targeted agent compared to triplet, respectively: PFS 13 months versus 8 months; OS not reached versus 11 months. Conclusions: KRAS c.35 G > A mutation may significantly affect worse OS of MCRC pts. It does not significantly affect worse PFS of intensive first line FIr-B/FOx, while after progression significantly affect worse efficacy of second line treatments. Re-challenge of intensive regimens may affect significantly favourable PFS and OS.