ESR1 and Familial prostate cancer: Studies show that BAP18 acts as an androgen receptor (AR) coregulator in prostate cancer, upregulating AR-mediated gene transcription and promoting prostate cancer progression (28); in estrogen receptor (ER)–positive breast cancer, BAP18 associates with the COMPASS complex, upregulating ER-mediated gene transcription, promoting ERα-positive breast cancer growth, and contributing to tamoxifen resistance (29).