MLH1 promotor methylation analysis is performed on tumour tissue to detect hypermethylation of the MLH1 gene promoter, adjunct to microsatellite instability (MSI), mismatch repair proteins MMR IHC, and for colon or endometrial tumours demonstrating MSI-H and loss of MLH1 protein expression. The absence of MLH1 promoter methylation is associated with an increased likelihood of germline mutation in a DNA mismatch repair protein.