Parallel sequencing of a 50 genes panel in metastatic colorectal cancer (MCRC) patients (pts) treated with intensive first-line FIr-B/FOx triplet chemotherapy plus bevacizumab (BEV): Preliminary data and clinical outcome.

644 Background: RAS/BRAF genotype guide MCRC treatment. First line triplet chemotherapy/BEV significantly improved PFS and OS. OS was significantly worse in KRAS c.35G > A and BRAF mutant (mt). Most CRC (86%) harbored mt genes, prevalently TP53, RAS, BRAF, PIK3CA. Methods: MCRC samples of 67 pts treated with FIr-B/FOx (77% overall) were analyzed through a 50 genes panel (PGM/Colon Lung Cancer) by ION Torrent: 57 (85%) primary, 10 (15%) metastatic samples; 59 (88%) pre-, 8 (12%) post-treatment. Molecular diagnostic criteria: > 50% coverage; > 1% mutant allelic fraction. Clinical outcomes were evaluated and compared by log-rank. Results: All wild-type (wt) and mt MCRC were 6 (8.9%) and 61 (91.1%), respectively; median mt genes 3 (1-12). Mt genes, 35 (%): KRAS 44 (65.6%), TP53 38 (56.7%), APC 26 (38.8%), KIT 23 (34.3%), PDGFRA 19 (28.3%), PIK3CA 18 (26.8%), EGFR and NRAS 15 (22.3%), SMAD4 10 (14.9%), FBXW7 and MET 7 (10.4%), GNAS and PTEN 6 (8.9%), BRAF and NOTCH1 5 (7.4%), ATM, PTPN11 and SMARCB1 4 (5.9%), HRAS, KDR, JAK3 and VHL 3 (4.4%), ERBB2, FGFR2, FGFR3, IDH1 and STK11 2 (2.9%), ABL1, AKT1, CDKN2A, FGFR1, FLT3, HNF1A, RB1, RET 1 (1.4%). BRAF mutations: c.1756G > A, 1796C > T, 1405G > A, 1406G > C. Median follow-up 21 months (m), overall PFS 13, OS 27m: KRAS exon 2 ( KRAS2) wt/mt, PFS 14/12m, OS 28/21m, respectively, not significantly different; c.35G > A KRAS mt showed trendly worse OS 14m; BRAF mt significantly worse PFS (8 vs 14m, p .026) and OS (11 vs 28m, p .002); RAS2-4/ BRAF15 wt/mt, PFS 18/13m (p .954), OS 28/22m (p .956). TP53 wt/mt, PFS 14/12m, OS 28/23m. All wt, PFS 24, OS 44m, not significantly different vs ≥ 1 mt gene. Conclusions: Multigenic analysis of MCRC patients treated with FIr-B/FOx shows worse clinical outcome conferred by uncommon BRAF mutations.

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.

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.