e15065 Background: Colorectal cancer (CRC) is a heterogeneous disease. Specifically for patients with BRAF-V600E mutations and/or mismatch repair deficiency or microsatellite instability-high (dMMR/MSI-High), there have been significant advances in terms of treatment options. Early identification of these subsets of patients has both prognostic and predictive value. We wanted to highlight an observation of utilizing 2 simple, rapid and universally available lab tests i.e. carbohydrate cancer antigen 19-9 and carcinoembryonic antigen tumor markers, the ratio (CA-19-9/CEA) of which can distinctly identify these patients. Methods: We included and analyzed the ratio of CA-19-9/CEA levels in patients with metastatic CRC at Mayo Clinic from December 2016 to February 2019, where both the results were available. Non-parametric tests were done to compare and contrast the differences in the median ratio and tumor marker levels. Results: BRAF-V600E mutant CRC patients had a discordantly profound elevation in CA-19-9 levels as opposed to the CEA levels. The median CA-19-9/CEA ratio was 20 (range: 0.3-167.3) in BRAF-V600E MSS patients as opposed to 4.40 (range: 0.003-216.2) in all other patients, p-value of 0.007 (Table). Similarly, the mean CA-19-9/CEA ratio for BRAF V600E MSS tumors was 57.15 (S.D.± 62.76) versus 10.5 (S.D.± 33.90) for all other types. Furthermore, this discordant elevation is not seen in BRAF-mutant MSI-High or any MSI-High patients (median CA-19-9/CEA ratio - 0.46). Conclusions: To date, this is the first report utilizing the ratio of tumor markers CA-19-9/CEA as predictive rather than just prognostic markers. It clearly identifies BRAF-V600E MSS and the MSI-High CRC patients from other subsets.[Table: see text]