For example, the following events are involved in malignant transformation of the endometriosis: the hypermethylation of the human mutL homolog 1 (hMLH1) gene promoter which causes a decrease in DNA mismatch repair gene expression, the hypomethylation of long interspersed element-1 (LINE-1), inactivation of the tumour suppressor genes runt-related transcription factor 3 (RUNX3) gene and Ras-association domain family member 2 (RASSF2) gene by their promoter hypermethylation [39]. This evidence concerns the gene MLH1 and endometriosis.