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); RAS_2-4/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.