365P Prognostic value of Lynch syndrome, BRAFV600E and RAS mutation status in dMMR/MSI-H metastatic colorectal cancer in a pooled analysis of the national Dutch and French cohorts

Current knowledge on biomarkers (BRAFV600E/RAS mutations) is mainly based metastatic colorectal cancer (mCRC) patients with proficient mismatch repair (pMMR) tumors. It uncertain whether these have the same implications in deficient (dMMR) mCRC patients. Our aim to provide insight value of Lynch syndrome, BRAFV600E and RAS mutation status treatment regimens survival dMMR treated outside clinical trials. This observational cohort study combined national Dutch cohort, including almost all centers (2014-2019), French 18 (2007-2017). Clinical, molecular data were collected tumors receiving chemotherapy ± targeted therapy. Multivariable Cox proportional hazard regression was used analyze prognostic syndrome progression-free (PFS) overall (OS). Inverse probability weighing impact survival. In our large real-world evidence 707 patients, 438 first-line systemic Mean age 61.9 years 40% had a proven/suspected syndrome. Most right-sided (74%) synchronous metastases (62%). mutations observed 42% 33%, respectively. Median PFS OS 6.0 months 19.3 from start analysis showed known pathological characteristics as predictors for PFS, but not or RAS. addition, there no differences according type chemo- therapy used. are associated poor prognosis contrast pMMR findings may aid estimating decision-making