Tumor sideness and mutational status: The potential effects on mCRC pts survival and treatment outcomes.

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682 Background: The treatment of mCRC has been changed with identification of different clinical behaviour of right and left sided tumors. Right-sided primary was associated with high mutational burden, worse prognosis and poor anti-EGFR response. We aimed to investigate the association between tumor site and survival, mutational status and treatment outcome of mCRC pts. Methods: The data of mCRC pts in two-cancer center in South Anatolia were retrospectively analyzed. The effects of tumor sidedness, treatment, braf on survival of mCRC pts were investigated using the log rank test. The Kaplan- Meier survival estimates were calculated. Results: A total of 210 (F/M=128/82) pts were included to study. Median age was 59.5 (range: 23-88) years. Right and left-sided tumour rates were 45 (21.7%) and 153 (72.9%), respectively. Kras, nras and braf mutation rates were 32.9, 5.5 and 6.7 %, respectively. Median follow-up was 27.5 (range: 1.3-274.3) months. In the right-sided tumors, kras (52.5 vs. 33.8 %, p=0.0034) and braf (33.3 vs. 11.1%, p=0.022) mutation rates were more than left-sided ones. Median PFS (15.1 vs. 14.2 months) and OS (27.5 vs. 23.9 months) were higher in the pts with left-sided tumors, the difference was not significant. First line bevacizumab was used in 76 (55%) in left, 15 (36%) in right, anti-EGFR was used in 27 (20%) in left, 11 (25%) in right-sided tumors. According to tumor side, there was no significant survival difference between treatment arms. In the pts with left-sided tumors, median OS was 39.3 months with anti-EGFR, 27.3 months with bevacizumab. Right-sided primary was associated with worse survival. Median OS was similar between braf wild and mutant tumours. Conclusions: Our mutation rates were similar with the literature. Braf mutations were more frequent in right-side tumors. Right-sided primary was associated with poor prognosis. However, the survival difference was not significant. Best survival rates were found with first-line anti-EGFR treatment in the pts with left-sided tumors, but only 20% pts used anti-EGFR at first line in this group. Due to low anti-EGFR usage at first line, survival rates were similar between treatment arms.