Withholding anti-EGFR, the impact on outcome in RAS wild-type metastatic colorectal tumors (WAIT or ACT trial).
626 Background: 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 propensity score to deal with potential confounders. Results: A total of 262 patients were included, 129 in the immediate anti-VEGF group and 133 in the delayed anti-EGFR group. Median follow-up was 37.9 months. Ninety-two patients had the anti-EGFR introduced at C2, 40 at C3. The median delay of RAS analysis was 19 days (q1-q3: 13-26). Patients treated with anti-VEGFs were more likely men (68% versus 56%), with more metastatic sites ( > 2 sites: 15% versus 9%). A propensity score including the number of metastatic sites and a possible previous treatment was built. Delayed anti-EGFRs were associated with longer PFS compared to immediate anti-VEGFs: 13.8 versus 11.0 months, p = 0.0244. After weighting, delayed anti-EGFRs were still associated with better PFS: HR 0.74, 95%CI [0.61 – 0.90], p = 0.0024. OS was not different between the two arms (30.5 for anti-VEGF versus 29.9 months, p = 0.3934), even after weighting (HR 0.86, 95%CI [0.69 – 1.08], p = 0.2024). There was a better RR with delayed anti-EGFRs: 66.7% versus 45.6%, p = 0.0007. Conclusions: Our findings suggest that, while waiting for RAS status, the delayed introduction of the anti-EGFR is a valid option, compared to the immediate introduction of the anti-VEGF.