The somatic single nucleotide mutations observed in MLH1 and MSH2 matched the mutational contexts associated with SBS18 and SBS36 (Pat_301:TCT>TAT and TCC>TAC; Pat_315:TCA>TTA), suggesting the constitutionally defective MUTYH contributed to these somatic MMR mutational events and resulted in MMR-deficiency in these two CRCs. The gene discussed is MLH1; the disease is mismatch repair cancer syndrome 1.