By Saumya Joseph

(Reuters) – Amarin Corp Plc’s fish oil-derived drug received a largely positive review from FDA staffers on Tuesday, dispelling investor fears that the company’s choice of placebo in its trial could challenge the approval of its potential blockbuster.

Shares of the company jumped 18% to $19.97 ahead of the drug’s evaluation on Thursday by an expert panel of advisers to the U.S. Food and Drug Administration.

A late-stage trial last year showed Vascepa cut the combined rate of heart attacks, strokes and other cardiovascular events by 25%.

But some experts argued the use of mineral oil as placebo in Amarin’s trial worsened bad cholesterol levels in patients or affected the absorption of the statin cholesterol drugs they were on, which could have skewed results in favor of Vascepa.

Vascepa, Amarin’s only drug, originally won U.S. approval in 2012 to lower high levels of triglycerides — a type of blood fat that can increase the risk of heart disease.

Amarin is now seeking to include on the treatment’s label its benefits of reducing the chance of heart attacks and strokes in patients with cardiovascular disease.

FDA staffers on Tuesday said their tests were inconclusive on whether the use of mineral oil as placebo could have impacted results.

While they could not rule out the possibility that mineral oil interfered with statin absorption, they said any interaction between the placebo and statin was expected to be minimal.

“We do believe everything should be subject to scientific scrutiny, but I think this (the concern) is something that Wall Street has created rather than science – I suspect the comments of the FDA will largely dispel that,” Chief Executive Officer John Thero told Reuters.

The big question around approvability due to use of mineral oil looks to be unlikely to cause any issues for label expansion, said Jefferies analyst Michael Yee.

An expanded label for the drug could open up a market of nearly 15 million Americans who have high triglycerides and other cardiovascular risk factors, despite being on statin treatment to lower cholesterol.

Roth Capital Partners analyst Yasmeen Rahimi expects Vascepa to capture about 12.1% of the market over the next decade, resulting in peak U.S. sales of $3.2 billion by 2030.

“The Street was a little nervous about what could be thrown their way. Now the surprise is gone,” said Rahimi.

Amarin recorded revenue of $229.2 million last year.

(Reporting by Saumya Sibi Joseph and Trisha Roy in Bengaluru; Editing by Maju Samuel and Shinjini Ganguli)