The Effect of Tumor Sideness and Mutational Status on First Line Treatment Response and Survival in The Patients with Metastatic Colorectal Cancer

RAS and BRAF mutation and primary tumour sideness are prognostic and predictive factors in metastatic colorectal cancer (mCRC). We aimed to investigate RAS-BRAF mutation rates and responses to biologic agents the effects of tumour sideness on survival. This was a retrospective study conducted at three Turkish institutes. 303 patients with mCRC who were examined for tumour RAS and 172 examined for tumour BRAF mutations between 2006-2018. A total of 303 (M/F= 186/117) patients were included to study. Median age was 63 (range: 23-86) years. Median follow-up was 22.8 (range: 19.1-26.4) months. In the RAS wild type population; addition to anti-EGFR agents to standard chemotherapy (CT) had better outcomes than Bevacizumab+CT. Median PFS was improved with anti-EGFR agents (Respectively PFS; 14.5 months, 8.7 months) (log rank p= 0.007 HR= 0.59). Median OS was similar between CT+anti-EGFR and CT+Bevacizumab arms (Respectively OS; 29.3 months, 21.7 months) (log rank p= 0.418; HR= 0.75). RAS mutation rates were similar between right colon cancer (RCC) and left colon cancer (LCC), BRAF mutation rates were significantly increased in RCC (22.2 vs 2.7%, p< 0.0001). RCC (24.1%) had worse prognosis than LCC (75.9%). However, this difference was not significant (PFS: 10.4 vs 10.0 months (log rank p= 0.136) , OS: 21.5 vs 23.1 months (log rank p= 0.436). We concluded that in the patients with RAS wild type tumours, CT and anti-EGFR combination was reasonable approach for first line treatment. BRAF mutation, irrespective of CT regimen, was associated with poor survival and more common in RCC patients.