The U.S. Food and Drug Administration granted accelerated approval to Clovis Oncology Inc's ovarian cancer drug in patients with a specific gene mutation whose disease had advanced despite two or more rounds of chemotherapy.

The drug, rubraca, which secured approval about two months earlier than scheduled, targets patients whose tumors have a mutation called BRCA, identifiable using an FDA-approved companion diagnostic test.

When a drugmaker wins accelerated approval, it must provide further evidence of the drug's benefit, failing which the approval can be revoked.

The FDA also approved on Monday a test made by Foundation Medicine Inc to help detect the presence of BRCA mutations. If one or more mutations are detected, the patient is eligible for rubraca.

About 15-20 percent of ovarian cancer patients have the BRCA mutation, the FDA said.

Rubraca is expected to compete against Tesaro Inc's niraparib and AstraZeneca Plc's lynparza. Tesaro applied for U.S. marketing last month after data released in October showed niraparib improved outcomes for all women with recurrent ovarian cancer.

All three drugs belong to a closely watched class of new medicines called PARP inhibitors, which block enzymes involved in repairing damaged DNA, thereby helping to kill cancer cells.

Lynparza became the first of the new class of drugs to reach the market when it won U.S. approval for ovarian cancer in 2014. The drug generated sales of $156 million in the first nine months of this year.

With a broader label than lynparza, Clovis now has the opportunity to establish a larger foothold ahead of competitive entrants in the maintenance setting, Piper Jaffray's Joshua Schimmer said in a note.

Maintenance therapy immediately follows initial treatment to keep patients cancer-free if they go into remission.

Niraparib and lynparza are both positioned to enter the maintenance setting ahead of rubraca, and how the competitive dynamic evolves remains to be seen, Schimmer said.

Rubraca is expected to generate sales of $267 million in 2018, according to brokerage Janney Montgomery Scott.

Other drugmakers, including AbbVie and Medivation, which was recently bought by Pfizer Inc for $14 billion, also have PARP inhibitors in development.

Clovis's shares doubled in late-September, after the company said rubraca would be reviewed on a priority basis, and the FDA would make its decision by Feb. 23.

Clovis's shares soared as much as 26 percent to $46.97 after trading resumed. Tesaro's shares fell about 4 percent to $126.07.