Distinguishing features of endometrial pathology after exposure to the progesterone receptor modulator mifepristone

There is growing interest in the use of progesterone receptor modulators such as mifepristone for treatment of gynecologic and other conditions, but interest in progesterone receptor modulators is dampened by the effects of the agents on the endometrium. In this study, we examined the endometria of women exposed to mifepristone for treatment of leiomyomas in doses of 2.5 and 5 mg and compared them to unexposed endometria. We assessed the reliability of these features by comparing agreement in ratings between pathologists who were blinded to each other's readings. We assessed distinguishing features between exposed and unexposed groups by comparing frequency of features between groups. We found that key features could be reliably assessed by pathologists experienced in endometrial pathology. We observed several features (nonsynchronous endometrium, large fluid filled glands, and abnormal blood vessels) that distinguished endometrial samples that were and were not exposed to the drug. These findings suggest several features that can be tracked during studies involving mifepristone and, potentially, other progesterone receptor modulators.