KLF9 and endometriosis: In this regard, P4 resistance is also a hallmark of endometriosis, and reduced/loss of KLF9 expression in uterine endometrial cells in KLF9 null mice, resulting in increased ectopic lesion establishment (45), and in women with endometriosis (46), was associated with loss of PGR-B expression (by contrast to PGR-A in myometrium) and deregulated expression of a subset of PGR-B target genes.