When SAG was administered to rescue P4 resistance and/or insensitivity in Cfp1d/d ectopic uterine lesions, P4 suppressed the size of Cfp1d/d ectopic lesions in the endometriosis model (Fig. 4b–e), suggesting that CFP1 is required for proper P4 responses to suppress ectopic growth of uterine tissues in mice. This evidence concerns the gene SAG and endometriosis.