MLH1 and Lynch syndrome: Tumors with abnormal expression of MLH1 by IHC were most likely to be of somatic origin because 54% (22/41) were attributed to MLH1 promoter hypermethylation and 17% (7/41) were attributed to double somatic events in MLH1. Notably, methylation of the MLH1 promoter was found in 3 of 7 MLH1-deficient Lynch syndrome–related tumors.