On Friday, Clovis Oncology (NASDAQ:CLVS) gained Food and Drug Administration approval of Rubraca for patients with metastatic castration-resistant prostate tumors that have BRCA mutations.

Rubraca inhibits poly ADP-ribose polymerase (PARP) proteins that are involved in the repair of DNA. By itself, inhibition of PARP doesn't do much, but inhibiting the repair proteins in the presence of mutations in BRCA proteins, which are also responsible for repairing DNA, results in enough damage to cancer cells' DNA that the tumor cells ultimately die.

Doctor talking to a patient in an exam room

Image source: Getty Images.

In the pivotal clinical trial used to gain FDA approval, 44% of patients with BRCA prostate cancer responded to Rubraca, defined as a shrinking of the prostate tumor without progression of bone tumors. When looking at tumors via prostate specific antigen -- a measure of prostate cancer cells -- Rubraca produced a 55% response rate.

Rubraca is already approved for ovarian cancer, where the drug produced $42.6 million in sales during the first quarter of 2020. While the drug is far from a blockbuster, sales were up 8% quarter over quarter and 29% year over year, suggesting there's still some growth left in ovarian cancer as Clovis Oncology competes with PARP inhibitors GlaxoSmithKline's (NYSE:GSK) Zejula and AstraZeneca (NYSE:AZN) and Merck's (NYSE:MRK) Lynparza.

Prostate cancer offers additional upside for Clovis where 12% of men with metastatic castration-resistant prostate cancer have mutations in one of the BRCA genes, although many of those patients may end up being treated with Rubraca after the use of traditional chemotherapy agents.