Tumor location in patients with colorectal cancer treated with bevacizumab

Introduction: The tumor location has proved to be a prognostic factor in patients with metastatic colorectal cancer, showing higher survival rates the left colon tumors than right colon tumors. However, the predictive value of response to different biological drugs is controversial. It has been published in recent essays the retrospectives of wild type (wt) RAS patients, that shows the efficacy of monoclonal antibody against epidermal growth (EGFR) for tumors confined to the left colon. Nevertheless, the results for bevacizumab regarding the impact on tumor location have been challenged. Methods: We retrospectively analysed data from 93 patients with metastatic colorectal cancer treated at our clinic from 2011 to 2016. The main objective was to define the overall survival (OS) in patients with metastatic colorectal cancer treated at first line with bevacizumab and compare to the the survival in terms of the RAS status and location of the primary tumor. Results: Patients average age was 62 years (31-79), 66% Male y 34% Female. All were classified as ECOG 0-1. Each patient received fluorouracil, oxaliplatin and bevacizumab as a first line treatment. 79% of the patients had hepatic metastases, 60% metastases in other locations and 40% both in the liver and other locations metastases. In 80% of the cases, the primary location of the tumor was in the left and in 20% in the right (including right and transverse colon). The average OS was of 22 months (IC 95%), being that 13 months in the right colon and 29 months in the left colon, but this numerical difference was not statistically significant (p = 0.070). The OS at 3 years was 38% in the left colon and 21% in the right colon. The survival was analyzed according to RAS mutation. Since this is a retrospective analysis, we do not have NRAS data from all patients. In the right colon 12% were wt RAS, 76% mutated and 12% wt KRAS/unknown NRAS. The OS was 20 months in wt RAS, 13 months in mutated RAS and 10 months in wt KRAS/unknown NRAS. The differences observed were not statistically significant (p = 0,485). In the left colon 45% were wt RAS, 34% mutated and 21% wt KRAS/unknown NRAS. The OS was of 37 months for wt RAS, 31 months for mutated RAS and 26 months for wt KRAS/unknown NRAS. The differences observed were statistically significant (p = 0,55). Conclusion: Our analysis confirms the highest percentage of RAS mutations in the right colon tumors. Although OS was higher for patients with colorectal cancer located on the left, the differences were not statistically significant, indicating that the impact of bevacizumab on survival outcomes are independent of the tumor location and RAS mutations.