Shares of Amgen Inc. were down 1.4% in premarket trade Monday after the company was downgraded to in-line from outperform by Evercore ISI, with analyst Umer Raffat citing patent concerns. Amgen stock's strong performance since 2011 has largely been due to a delay in biosimilar competition, Raffat said in a note to investors, but that is no longer the case. A court decision on Amgen's biggest drug, Enbrel, is imminent, and a biosimilar by Novartis's Sandoz already has tentative approval, Raffat said. Shares of Amgen have gained 2.1% in the year to date through Friday, while the iShares Nasdaq Biotechnology ETF has gained 13.5%. The S&P 500 has gained 6.3%.