As such, LIF mRNA and protein, both content and localization within the endometrium, have been studied in a variety of infertility cohorts including unexplained infertility (11, 12), recurrent implantation failure (13, 14), as well as in diseases associated with infertility such as adenomyosis (15, 16) and endometriosis (6, 7). This evidence concerns the gene LIF and endometriosis.