AstraZeneca (NYSE:AZN) and Merck (NYSE:MRK) continue their quest to gain additional approvals for their blockbuster cancer drug Lynparza. The duo submitted a new application to the Food and Drug Administration for the drug as a treatment for prostate cancer that's resistant to androgen depletion therapy and has metastasized to other areas of the body.

The FDA gave the application a priority review, which cuts four months off the review cycle. The pharmaceutical companies expect to hear back from the agency in the second quarter of this year although a decision could come earlier.

Doctor talking to a patient at a table

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Lynparza inhibits poly (ADP-ribose) polymerase (PARP) proteins that are responsible for repairing nicks in DNA. Inhibition of PARP proteins results in DNA breaks that would normally be repaired through homologous recombination, so AstraZeneca and Merck tested the drug specifically in patients with mutations in genes responsible for homologous recombination repair.

The application is based on the results of the PROfound clinical trial that tested two groups of prostate cancer patients. In patients with mutations in BRCA1/2 or ATM, Lynparza reduced the risk of disease progression by 66% compared to patients taking either Johnson & Johnson's (NYSE:JNJ) Zytiga or Astellas Pharma and Pfizer's (NYSE:PFE) Xtandi. Lynparza also extended the time it took the disease to progress while the patient remained alive from a median of 3.6 months for Zytiga or Xtanti to 7.4 months for Lynparza.

In the overall population that included patients with mutations in other homologous recombination genes, Lynparza reduced the risk of progression by 51% and extended median progression-free survival to 5.8 months, compared to 3.5 months for patients receiving Zytiga or Xtanti.

Lynparza is approved for ovarian, breast and pancreatic cancer. AstraZeneca booked Lynparza sales of $847 million in the first nine months of 2019.