Biogen (BIIB 0.85%) released its first-quarter earnings report before the market opened on Wednesday, reporting $3.5 billion in revenue, a 1% year-over-year increase. Sales of the multiple sclerosis drug Tecfidera, which is the biotech company's best-selling product, grew 10% to $1.1 billion. And Spinraza, its treatment for spinal muscular atrophy, recorded revenue of $565 million, up 9% compared to the prior-year quarter. 

Biogen's revenue got a $100 million boost as a result of accelerated sales propelled by the COVID-19 pandemic. The company's GAAP net income was $1.4 billion, or $8.08 per share basis. Its net income decreased by less than 1% compared to the year-ago period, while its earnings per share increased by 13%.

Doctor with a confused facial expression and his hands raised in the air.

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However, arguably the most crucial part of Biogen's report was an update regarding its potential treatment for Alzheimer's disease, aducanumab, which the company is developing in collaboration with Esai (ESALY 0.24%). In March 2019, Biogen discontinued the development of aducanumab because it had not demonstrated  effectiveness against the symptoms of Alzheimer's in a phase 3 clinical trial. However, in October, Biogen announced that it would seek regulatory approval for aducanumab after all. 

According to the company, a more extensive data set revealed that Alzheimer's patients treated with aducanumab experienced "significant benefits on measures of cognition and function." Biogen had planned to submit aducanumab to the Food and Drug Administration for review in early 2020.

Now, the biotech giant says it expects to complete its FDA filing for aducanumab in the third quarter of 2020. Biogen's stock slid by about 9.4% on Wednesday, likely in reaction to the delay.