Flores VA, et al. - In this retrospective cohort study, researchers tested the premise that progesterone receptor (PR) levels in endometriotic lesions determine response to progestin-based therapy by analyzing data of 52 subjects with histologically confirmed endometriosis and a previous documented response to hormonal therapy. It was noted that the threshold of PR > 80 was correlated with a 100% positive predictive value whereas the threshold of PR < 5 was related to a 94% negative predictive value. A strong association was found between PR status and response to progestin-based therapy. Findings suggested that endometriosis receptor status could be used to tailor hormonal-based regimens after surgery and negate trialing progestin-based therapy to determine resistance. Ascertainment of PR status can lead to a novel, targeted, precision-based approach to treating endometriosis.