ESR1 and breast cancer: The authors further proposed that “the combined effects of mifepristone and estrogen receptor modulators warrant clinical evaluation to improve endocrine treatment responsiveness in these patients.” This recent report supports earlier studies (19–21), including pre-clinical studies from our laboratory (22, 23), that proposed the combined use of an antiestrogen and the antiprogestin, mifepristone, to more effectively kill breast cancer cells and circumvent the development of antiestrogen resistance in ER+ breast cancer.