Withholding Anti-Egfr, The Impact On Outcome In Ras Wild-Type Metastatic Colorectal Tumors (Wait Or Act Trial).

626Background: First line of RAS wild-type (WT) unresectable metastatic colorectal cancer (mCRC) can be doublet chemotherapy with an anti-VEGF (Vascular Endothelial Growth Factor), or an anti-EGFR (Epidermal Growth Factor Receptor). Waiting for RAS status, many oncologists initiate chemotherapy and add the anti-EGFR secondly. The objective was to compare the delayed introduction of the anti-EGFR to the immediate introduction of the anti-VEGF in first-line treatment of RAS WT mCRC. Methods: This was a retrospective cohort analysis from 2013 to 2016, multicentric with 28 health care centers. We included patients with RAS WT unresectable mCRC treated between 2013 and 2016 by a doublet chemotherapy with the anti-VEGF introduced immediately or with the anti-EGFR introduced at C2 or C3. Progression free survival (PFS), overall survival (OS) and response rate (RR) for the two cohorts were compared. Hazard ratios (HR) with 95% confidence interval (95%CI) were estimated with cox regression models weighted on prope...