Impact of RAS/BRAF mutation status in locally advanced rectal cancer treated with preoperative chemotherapy.

PURPOSE: Our sincere hope is to establish the predictive factors of neoadjuvant chemotherapy (NAC) response and provide patients with greater certainty regarding treatment outcomes. The aim of this study was to assess the response to NAC and survival in patients with locally advanced rectal cancer (LARC) according to their RAS/BRAF mutation status. METHODS: Data on 57 patients with LARC who received NAC between 2009 and 2016 were analyzed retrospectively. The patients were classified into two groups based on their mutation status: wild-type in both RAS and BRAF (WT) or mutant-type in either RAS or BRAF (MT). RESULTS: Twenty-three patients were classified as WT, and the remaining 34 patients were MT. Histological response to NAC was similar in both groups. In responders, the 3-year relapse-free survival (RFS) was better compared with the non-responders (92 and 66%, respectively). In the WT group, the 3-year RFS was 95% which was significantly better than that in the MT group (59%, p = 0.011). The MT group was further subdivided into the following 2 groups by the pathological response; the MT responders (n = 10) and MT non-responders (n = 24). The 3-year RFS was 50% in the MT non-responders, which was significantly worse compared to that in the remaining patients (92%, p = 0.001). CONCLUSION: RAS/BRAF mutations did not affect the response to NAC. However, the RFS was likely to be poor for those in the MT group who did not achieve favorable pathological response. In contrast, the RFS was favorable in the WT group regardless of the pathological response.