Shares of Biogen /zigman2/quotes/201531540/composite BIIB -1.78% jumped 7.4% in premarket trading on Wednesday after the drugmaker and Eisai Co. Ltd. [: j:4523] said they completed the submission to the Food and Drug Administration for their experimental Alzheimer's disease drug. The therapy, aducanumab, has had a somewhat complicated path to this point; more than a year ago, Biogen scrapped development plans for the investigational drug after an analysis indicated that the drug wouldn't meet the endpoints in a late-stage clinical trial. Then in the fall, to the surprise of investors, Biogen announced that it would seek FDA approval. However, some analysts have remained skeptical about whether the regulator will approve the therapy. Biogen's stock is down 9.5% year-to-date. The S&P 500 /zigman2/quotes/210599714/realtime SPX +0.27% has declined 2.6%.