AstraZeneca's (AZN - Get Report) Lynparza significantly delayed the recurrence of tumors in patients with ovarian cancer compared to a placebo, according to results from a phase III study announced by the company Wednesday.

Lynparza belongs to a closely followed class of cancer drugs known as PARP inhibitors. Wednesday's positive study results, if confirmed, position Lynparza for expanded U.S. approval as a maintenance therapy in ovarian cancer.

This is the same indication Tesaro (TSRO is seeking as the first approval for its competing PARP inhibitor niraparib, based on data presented earlier this month.

AstraZeneca is withholding specific data from the Lynparza ovarian cancer maintenance therapy study, so making comparisons to Tesaro's niraparib isn't possible quite yet.

What we do know, thanks to AstraZeneca's limited disclosure Wednesday, is that Lynparza "substantially exceeded" results seen in a previously conducted phase II maintenance study.

In that phase II study, which enrolled ovarian cancer patients with mutation to a tumor suppressor gene known as BRCA, treatment with Lynparza demonstrated an 82% reduction in the risk of tumor progression compared to placebo. At the median, Lynparza progression-free survival was 11.2 months compared to 4.3 months for placebo.

Lynparza is already approved in the U.S. as a treatment for ovarian cancer patients with BRCA mutant tumors no longer responsive to three or more prior therapies. In Europe, Lynparza is approved as a second-line maintenance therapy for ovarian cancer patients with BRCA mutated tumors.

AstraZeneca's plan is to expand Lynparza's marketing label in the U.S. to include maintenance therapy for ovarian cancer, a larger commercial opportunity, based on the data from the phase III study announced Wednesday.

Racing AstraZeneca to the FDA will be Tesaro, which is expected to file a new drug application before the end of the year for niraparib as a maintenance therapy for ovarian cancer.

Adam Feuerstein writes regularly for TheStreet. In keeping with company editorial policy, he doesn't own or short individual stocks, although he owns stock in TheStreet. He also doesn't invest in hedge funds or other private investment partnerships. Feuerstein appreciates your feedback; click here to send him an email.