What happened

According to data from S&P Global Market Intelligence, shares of Clovis Oncology (NASDAQ:CLVS) gained 7.42% in March. The drugmaker's shares are now up almost 28% so far this year due to the Food and Drug Administration's (FDA) approval of its advanced BRCA-mutant ovarian-cancer drug Rubraca last December.

This approval marked the second for a PARP inhibitor for advanced ovarian cancer, with AstraZeneca's (NYSE:AZN) Lynparza hitting the market first in 2014. PARP inhibitors function by interfering with a cell's ability to repair its DNA, leading to genomic instability and cell death. 

Doctor examining an x-ray.

Image Source: Getty Images.

So what

From a fundamental perspective, Rubraca should go a long way toward improving Clovis' outlook. With a high-end 2018 sales estimate of $462 million, for instance, Clovis could become a cash-flow-positive operation as early as next year.

Now what

The next shoe to drop is Rubraca's mid-year data release for its ongoing maintenance therapy study, dubbed "ARIEL 3."

Unfortunately for Clovis and its shareholders, though, Astra's Lynparza is currently under priority review with the FDA as a maintenance therapy in ovarian cancer, and Tesaro's (NASDAQ:TSRO) rival PARP inhibitor Zejula gained an early approval -- along with a far broader label than Rubraca -- just this week.

The point is that the advanced ovarian-cancer market is starting to get a tad crowded, and it's not altogether clear which drug will emerge as the market-share leader. Tesaro's drug, nonetheless, appears to have the best chance at grabbing the lion's share of the market based on its particularly strong clinical profile that prompted the FDA to approve it three months ahead of schedule. 

Clovis' run-up following Rubraca's approval may not be entirely warranted. Rubraca, after all, will have to overcome some stiff competition to justify the company's present valuation.

George Budwell has no position in any stocks mentioned. The Motley Fool has no position in any of the stocks mentioned. The Motley Fool has a disclosure policy.