Prognostic importance of primary tumor location in RAS mutant metastatic colorectal cancer

Objective: The prognostic value of tumor location in patients with metastatic colorectal cancer (mCRC) was reported by recent analyses in RAS wild-type patients. However, there is no enough specific data regarding prognostic value of primary tumor location in RAS mutated mCRC patients. We aimed to find if there is any relation between tumor prognosis and primary tumor location in patients with RAS mutated mCRC. Method: This retrospective study included 57 patients with mCRC who were diagnosed and treated in our hospital between January 2011 and December 2017. Characteristics features of the patients were obtained from our institution patient medical records. Patients were included to the present study if KRAS or NRAS mutation was detected in tumor tissues. Results: Twenty-nine (50.9%) of patients were female and the median age of all patients was 52 (18-80) years. Forty (70.2%) of 57 patients were defined as left side (LS) and 17 (29.8%) of patients were located in the right side (RS). As first line systemic treatment, twenty-five (43.9%) patients had received oxaliplatin-based chemotherapy while 32 (56.1%) patients had received irinotecan-based chemotherapy. Tumor sidedness did not affect on PFS (mPFS, 10.9 months for LS vs 8.1 months for RS, p=0.400) and OS (mOS, 20.9 months for LS vs 20.8 months for RS, p=0.930).The patients who had oxaliplatin based chemotherapy regimens showed better OS rate than irinotecan based regimens (28.7months vs16.3 months, p=0.017, respectively). Conclusion: Our study results support the thought that claims the sidedness of primary CRC in metastatic setting does not have effect on PFS and OS in patients with RAS mutant mCRC. However, our findings also underline the necessity of studies with larger patient populations and subgroup analyzes to evaluate potential prognostic and molecular features to determine the standart approach to this specific subgroup of the disease.