MRC1 and rectal neoplasm: Furthermore, somatic mutations in MSH6 (c.3284G>A, c.676G>T) were also detected in the rectal tumors; however, similar somatic mutations were not detected in the extraintestinal tumors, suggesting that differences in the frequency and type of secondary mutation strikes suffered by the MMR gene among different organs may be a potential factor that triggers the atypical phenotype of dMMR and MSI (11, 12).