Baker Bros. Advisors LP, a healthcare-focused fund, added 11.4 million shares to its stake in Amarin Corp. PLC during the third quarter, according to a review of 13-F filings.

Baker Bros. owned over 34 million shares of Amarin at quarter-end, making it the Dublin-based biotechnology company's largest shareholder. At the end of September, Amarin completed its multi-year post-market study of Vascepa, an omega-3 fatty acid supplement. The trial showed that patients who received 4 milligrams of Vascepa per day reduced their heart-related risk by 25% when compared to placebo.

After the news broke, Amarin’s stock price jumped and ended the quarter at $16.27 per share, 426.5% higher than at the start of the quarter.

The majority of Baker Bros.' top holdings remained the same during the quarter, with 14 out of the 20 largest holdings showing no change in the number of shares owned. The fund did add over 1 million shares of ACADIA Pharmaceuticals Inc. and BioCryst Pharmaceuticals Inc., raising its stakes by 4.5% and 7.8% respectively. Sage Therapeutics Inc. was the lone company in the investment manager's top holdings to have shares sold.

Baker Bros. added eight new positions during the quarter, including five drugmakers — Principia Biopharma Inc., Y-mAbs Therapeutics Inc., Crinetics Pharmaceuticals Inc., Aquestive Therapeutics Inc., and Constellation Pharmaceuticals Inc. — that were launching their initial public offerings during the three months that ended Sept. 30. At $52.2 million, Baker Bros.' new stake in Principia Biopharma was the largest among the new positions initiated during the quarter.

Click here to view Baker Bros. Advisors LP current common stock holdings. Company filings including the 13F can be found through the filings archive tab on a company's briefing book page.