MLH1 and neoplasm: Therefore, in this study, we classified MSI tumours according to their methylation status in the MLH1 promoter; 2.9% (29/1,013) tumours with extensive MLH1 methylation were categorised as MSI with MLH1 methylation (MSI-M) and 3.6% (36/1,013) tumours without extensive MLH1 methylation as MSI with unmethylated MLH1 (MSI-U).