Background: Multiple studies have reported prognostic association of neutrophil to lymphocyte ratio (NLR), platelet to lymphocyte ratio (PLT) and albumin levels in patients (pts) with colorectal cancer. However, it is unknown the prognostic impact in patients with BRAF(V600) mutant metastatic colorectal cancer (mCRC). Methods: Observational, retrospective, multicentric study pts with BRAF V600mt mCRC treated at 9 university Spanish hospitals in NW Spain, belonging to GITuD Group. Demographic, clinic, pathological characteristics, overall survival (OS) and progression free survival (PFS) data were retrospectively collected and analyzed. We calculated a Systemic Inflammation Score (SIS) summing the number of risk factors that each patient had: albumin levels <3.6 g/dL, Hemoglobin levels <12.5, Neutrophil to Lymphocyte ratio (NLR) >3 and Platelet to lymphocyte ratio (PLR) >175. Results: We recorded data from 71 pts between November 2010 to June 2018. Median age was 62.0 years (range 31-83y), 54.9% female, 73.2% ECOG PS0-1, 49.3% right-sided, 37.3% high grade, 70.4% synchronous presentation, 64.8% primary tumor resection. Median OS was 11.9 months (m) (95% CI, 9.7-14.0 (m)). Pts with higher NLR (>3) had a significantly lower OS: 7.8 vs 13.7 (m) HR 1.934 (95% CI 1.2-3.3) p = 0.014, which was also true for pts with low Hb (<12.5g/dL): OS 9.0 vs 13.0 (m) (HR 1.767,95% CI 1.1-3.0 p = 0.035) and low albumin (<3.6 g/dL): OS 4.9 vs 12.5 (m) (HR 2.142; 95% CI 1.1-4.5, p = 0.040). Pts. with higher PLR (>175) was associated with a non-significant trend worse OS: 5.7 vs 13.5 (m) (HR 1.555; 95% CI 0.9-2.7, p = 0.102). SIS was associated with a worse prognosis: median OS 0/1/2/3/4 factors were 16.7 vs. 11.0 vs. 11.4 vs. 4.8 vs. 4.0 (m) (p = 0.006). Pts with SIS = 0 had significantly higher OS: 16.7 vs 9.0 (m) (HR 0.357; 95% CI 0.3-0.9; p = 0.027). First-line PFS was 4.4 (m) (95% CI, 3.2-5.7 months). First line PFS according type of treatment: Bev+Triplet-CT/Bev+Doublet-CT/antiEGFR+Doublet-CT/Doublet-CT: 8.0 vs 4.8 vs 2.9 vs 2.1 (m) (p = 0.091). BEV based CT was associated with a prolonged first line PFS: median 5.2 vs. 2.3 (m) (HR 0.562; 95% CI, 0.3-0.9; p = 0.033). BEV based CT was associated with prolonged first-line PFS in SIS Score 1-4: 4.8 vs. 2.3 (m) (HR 0.426; 95% CI 0.2-0.8; p = 0.009). Nevertheless, we don’t identify differences in first-line PFS in SIS Score 0: 7.0 vs 2.1 (m) (HR 0.803; 95% CI 0.3-2.5; p = 0.700). Conclusions: SIS identifies a population with a worse prognosis and subsidiary of improvement in First-line PFS with BEV based CT.