An extended-release (ER) formulation of onapristone, an orally bioavailable progesterone receptor (PR) antagonist, with antineoplastic activity. Onapristone binds to the PR and inhibits both PR activation and the associated expression of PR-responsive genes. This may inhibit PR-mediated proliferative effects in cancer cells overexpressing PR. PR is expressed on certain cancer cell types and plays a key role in proliferation and survival. Check foractive clinical trials using this agent.