Factors Affecting the Efficacy of Regorafenib in Metastatic Colorectal Cancer: Is Tumour Sidedness Important?

OBJECTIVE: To investigate the outcomes of regorafenib treatment in refractory metastatic colorectal cancer (mCRC) patients by primary tumour sidedness, the effects of previously targeted therapies, RAS status and inflammatory markers. STUDY DESIGN: Observational study. Place and Duration of the Study: Department of Medical Oncology, Karadeniz Technical University, Faculty of Medicine, Trabzon, Turkey, between January 2012 and September 2020. METHODOLOGY: Clinical data of 102 mCRC patients treated with regorafenib were compared according to the right and left colon subgroups, in terms of factors affecting outcomes of regorafenib treatment. Kaplan-Meier method was used to identify factors associated with the overall survival. RESULTS: Disease control rate (DCR) with regorafenib were similar in both right and left-sided colon tumours (60% vs. 61%, respectively, p>0.99). The median overall survival (OS) was 6.6 months in patients with right-sided colon cancers and 10.1 months in patients with left-sided colon cancers, but it was not significant (p=0.238). When evaluating by RAS status, there was an increase in favour of the right-sided mCRC in progression-free survival and OS, without statistical significance. In multivariate analysis, the patients with metastatic sites <3 and the number of prior systemic therapies ≤3 line had significantly higher survival. CONCLUSION: The tumour burden affected the response to regorafenib in subsequent treatments and regorafenib was also effective in heavily treated mCRC patients. There was no difference in PFS and OS in terms of tumour sidedness by regorafenib treatment. KEY WORDS: Colorectal cancer, Regorafenib, Tumour sidedness.