What is Apristor?

Apristor (Onapristone extended release) is an investigational drug, which means it is currently not FDA approved for the treatment of PR+ cancer.  It is a small molecule drug that blocks progesterone receptor-mediated activation of pro-survival signaling pathways in PR+ cancer cells. Apristor is a safer and more pharmacologically active version of onapristone. 

How Is It Given?

Patients take a 50 mg pill of Apristor every 12 hours with or without food.

Why Is Apristor Being
Studied In Cancer?

Apristor is being studied to see if blocking progesterone receptor activity halts metastatic cancer growth in PR+ patients.

What Results Have
Been Seen So Far?

Apristor is being studied and is not approved.  Apristor completed a previous Phase 1 study in PR+ cancer patients [Cottu 2018].  On average, study participants had progressed on multiple prior rounds of chemotherapy and hormonal therapy.  Apristor was well tolerated across dosing cohorts and 20% of patients (9 out of 46) achieved stable disease or better, including 1 complete response, for a duration of 6 to 10 months. 

The immediate release version of Apristor - Onapristone immediate release or "OnaIR" - has completed two previous Phase 2 studies in metastatic breast cancer patients. 

  • 1st Line Metastatic / Locally Advanced: 56% of patients saw their cancer shrink in size (Robertson, 1996)

  • 1st Line Metastatic / 2nd Line Endocrine: in patients who were progressing on tamoxifen, 48% saw their cancer stabilize or shrink after 6 months of treatment. In patients who were PR+, 56% (19 out of 33) saw their cancer stabilize or shrink after 6 months of treatment (Jonat, 1999)

There is no guarantee that patients will see a similar result should they enroll in ONWARD and receive Apristor. It is also not known whether or not the impact on tumor size will help patients live longer or have any other benefits.

Apristor is a drug being tested in clinical studies and has not been approved by the FDA.  It is not known if Apristor works or if it is safe.