Serum CA19-9 Response Is an Early Predictive Marker of Efficacy of Regorafenib in Refractory Metastatic Colorectal Cancer

Purpose: Regorafenib improves survival in chemorefractory metastatic colorectal cancer (mCRC) patients. However, regorafenib induces various adverse events (AEs) that often impair patients' quality of life. Identification of early predictive markers of the efficacy is warranted. Methods: We retrospectively examined 146 consecutive mCRC patients who received regorafenib. Clinical parameters, including patient background, AEs, and changes in biochemical parameters until day 28, were evaluated to identify efficacy predictors. Results: Median progression-free survival (PFS) was 2.1 months, and median overall survival was 6.6 months. Major AEs in all cycles were hand-foot skin reaction, hypertension, and increased aspartate transaminase. We extracted 121 patients for prognostic analysis. In univariate analysis, decreased carcinoembryonic antigen (HR: 0.570, p = 0.012) and decreased carbohydrate antigen 19-9 (CA19-9) (HR: 0.422, p = 0.0012) were identified as prognostic markers of PFS. Patients in whom serum CA19-9 decreased after regorafenib exhibited significantly better PFS (median 3.7 vs. 2.0 months, p = 0.004) than those in whom serum CA19-9 did not decrease. Multivariate analysis revealed early CA19-9 decrease as an independent predictive factor (HR: 0.415, 95% CI: 0.210-0.818, p = 0.011). Conclusion: Early response of CA19-9 may predict the efficacy of regorafenib. Additional studies are needed for external validation.