Federal health regulators are asking tough questions about the risk of tumors and heart problems with an experimental diet pill from Arena Pharmaceuticals, which was previously rejected for similar safety concerns.

The Food and Drug Administration denied approval for Arena’s lorcaserin in 2010 after scientists raised concerns about tumors that developed in animals studied with the drug. The company resubmitted the drug with additional data earlier this year, hoping for a better outcome.

But questions posted by the FDA on Tuesday, ahead of a public meeting later this week, show the agency still has safety concerns. The agency will ask a panel of advisers Thursday whether Arena has provided enough data to address the risk of tumors seen in animals. The agency will also seek expert opinions on new data about heart risks.

The FDA is not required to follow the advice of its advisers, though it usually does.

In reviewing the company’s reanalyzed animal data, the FDA concluded lorcaserin “minimally affected” levels of a hormone linked to breast development. FDA reviewers said it is “plausible” the increased hormone levels contributed to noncancerous tumors seen in female rats.

The quest for a blockbuster weight loss drug has eluded nearly every major pharmaceutical firm over the last four decades.

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With U.S. obesity rates nearing 35 percent of the adult population, many doctors say new pharmaceutical treatments are needed. And Wall Street analysts estimate that even a modestly effective drug has blockbuster potential.

But a long line of prescription weight loss offerings have been associated with safety problems, most notably the fen-phen combination, which was linked to heart damage in 1997. The cocktail of phentermine and fenfluramine was a popular weight loss combination prescribed by doctors, though it was never approved by FDA.

Arena is one of three small drugmakers racing to launch the first new prescription diet drug in more than a decade. The FDA has already rejected each of the drugs once and all three companies have resubmitted their products for a second review. Earlier this year, rival Vivus Inc. won a surprising endorsement from an FDA panel for its drug Qnexa, raising expectations for Arena and Orexigen Therapeutics Inc., the third company in the race.

Shares of San Diego-based Arena Pharmaceuticals Inc. rose 54 cents, or 19.9 percent, to $3.26 in morning trading.