Our study was done in order to identify novel molecular markers to predict which locally advanced rectal cancers (LARCs) might be resistant to neoadjuvant chemoradiotherapy (nCRT). Seventy-four patients with LARCs treated with nCRT were collected. Pathological evaluation after nCRT was performed according to the tumor regression grading (TRG) system. Next-generation sequencing kit including 279 exons of 59 genes was performed on Illumina Miseq Platform. Sanger sequencing was performed to confirm some mutations. Four of the tumors (4/74, 5.4%) had BRAF mutation, which presented in one TRG 2 tumor and three TRG 3 tumors but was not observed in TRG 0-1 tumors. Higher mutational frequency of BRAF gene in TRG 3 tumors (3/12, 25%) was found in comparison with the TRG 0-2 tumors (1/62, 1.6%; p = 0.012). Eight tumors (8/74, 10.8%) harbored SMAD4 mutations, which was mutated across all TRG groups. However, SMAD4 mutated more in TRG 3 tumors (4/12, 33.3%) compared with that in TRG 0-2 tumors (4/62, 6.5%; p = 0.020). The patients with BRAF-mutated LARCs had shorter progression-free survival (PFS) (p = 0.045) and shorter overall survival (OS) (p = 0.000) than the BRAF wild-type (WT) ones. The patients with SMAD4-mutated tumors had shorter PFS than the WT cases (p = 0.008). BRAF and SMAD4 genetic mutations might be important molecular markers to predict resistance to nCRT and poor prognosis in LARCs. More cases are needed to confirm these findings in the near future.
Keywords: BRAF; Neoadjuvant chemoradiotherapy; Predictor; Rectal cancer; SMAD4.