Progesterone Receptor Status Predicts Response to Progestin Therapy in Endometriosis

Progestin-based therapy is the first-line treatment for managing endometriosis-associated pain. However, response to progestins is currently variable and unpredictable. Predictive markers for response to progestin-based therapy would allow for a personalized approach to endometriosis treatment. We hypothesize that progesterone receptor (PR) levels in endometriotic lesions determine response to progestin-based therapy. Retrospective cohort study. Academic center. Fifty-two subjects with histologically confirmed endometriosis and a previous documented response to hormonal therapy were included. Immunohistochemistry was performed on sections of endometriotic lesions using a rabbit polyclonal IgG for detection of PR-A/B. The Histo (H)-score was used for quantifying PR status. Response to progestin-based therapies was determined from review of the electronic medical record. H-score was higher in responders compared with nonresponders. Subjects were categorized into three groups: high (H-score > 80, n = 7), medium (H-score 6 to 80, n = 28), and low (H-score ≤ 5, n = 17) PR status. The threshold of PR > 80 was associated with a 100% positive predictive value. The threshold of PR < 5 was associated with a 94% negative predictive value. PR status is strongly associated with response to progestin-based therapy. Receptor status in endometriosis could be used to tailor hormonal-based regimens after surgery, and negate trialing progestin-based therapy to determine resistance. Ascertainment of PR status may allow for a novel, targeted, precision-based approach to treating endometriosis.