Success in two pivotal studies of high dose Eylea (aflibercept) has significantly strengthened Regeneron Pharmaceuticals Inc.’s market position. But the company will face stiff competition from biosimilars and Roche Holding Group’s recently approved Vabysmo. After struggling for much of the year, the Tarrytown, N.Y.-based company’s stock (NASDAQ: REGN) rose about 20% this week. It closed 2% upward on Sept. 9 at $724.32 per share.