The acetate form of the 21-substituted-19-nor-progestin telapristone, an orally available selective progesterone receptor modulator (SPRM), with potential anti-progesterone and antineoplastic activities. Upon oral administration, CDB-4124 competitively binds to the progesterone receptor (PR) in progesterone-responsive tissue and inhibits PR-mediated gene expression. This interferes with progesterone activity in the reproductive system. As a result, this agent may suppress ovulation and inhibit proliferation of endometrial tissue. Also, this agent may prevent cell growth and induce apoptosis in estrogen receptor (ER) and PR-positive breast cancer cells through a reduction in progesterone levels, ER downregulation and a suppression of the expression of cyclin-dependent kinases (CDK) 2 and 4, ultimately leading to G1/S cell cycle arrest. Unlike some other SPRMs, this agent does not exert any estrogenic, androgenic, anti-estrogenic, and anti-androgenic activities.