MMEJ almost always involves at least a small deletion, so that it is a mutagenic pathway.[60] FEN1, the flap endonuclease in MMEJ, is epigenetically increased by promoter hypomethylation and is over-expressed in the majority of cancers of the breast,[61] prostate,[62] stomach,[63][64] neuroblastomas,[65] pancreas,[66] and lung.[67] PARP1 is also over-expressed when its promoter region ETS site is epigenetically hypomethylated, and this contributes to progression to endometrial cancer,[68] BRCA-mutated ovarian cancer,[69] and BRCA-mutated serous ovarian cancer.[70] Other genes in the MMEJ pathway are also over-expressed in a number of cancers (see MMEJ for summary), and are also shown in blue.