In a surprising update, Biogen announced Monday that its top scientist, Alfred Sandrock, who led development on some of the company's most important medicines, will retire at the end of the year.
In a letter to his colleagues, Sandrock, 64, wrote that it's time to "move on to the next chapter" in his life. He will be replaced on an interim basis by Priya Singhal, head of global safety and regulatory sciences, until Biogen selects a permanent successor.
Sandrock's departure comes at a difficult time for the company he's called home for more than two decades. Revenue has declined over the past two years, putting pressure on Biogen to bring new, lucrative products to market.
A closely watched and recently approved Alzheimer's drug was meant to be the company's answer. But so far, it hasn't lived up to expectations. Controversy surrounding the drug — which is known as aducanumab and sold as Aduhelm — has also led to a federal investigation of its expedited approval, along with criticism of Biogen's standards for collecting and analyzing scientific data.
What's more, Aduhelm's safety, which was already of particular interest to doctors and patients, is now even more in-focus after a 75-year-old patient who received the drug died. Biogen said it's investigating the death.
That Sandrock is leaving in the midst of these challenges reads, at least to some, as odd, especially given how much of a key player he was in the company's development and defense of Aduhelm. He is also set to leave Biogen about a month before the federal government makes a crucial decision on whether Medicare should cover Aduhelm nationwide.
"This strikes us as a rather abrupt departure, as we have had zero signal that was he was approaching an exit, particularly as he has been the most public voice at Biogen defending aducanumab's data and approval process," Brian Skorney, an analyst at Baird, wrote in a note to clients.
Biogen shareholders appeared unnerved by the news as well, as the company's share price slid by nearly 4% in Tuesday morning trading.
Others were less concerned. Stifel analyst Paul Matteis, for instance, argues said that, while sudden, Sandrock's retirement shouldn't be viewed as shocking.
"Sandrock's abrupt departure is of course optically — and literally — negative. But at the same time, we would imagine that being Biogen's R&D head right now is one of the most challenging and exhausting jobs in biotech, and Dr. Sandrock was late in his career," Matteis wrote in a note to clients.
News of Sandrock's departure was first reported by STAT News before being confirmed by the company.

During his time at Biogen, Sandrock held several high-ranking positions, with the most notable being that of chief medical officer from 2012 to 2020 and head of research and development since late 2019. In those roles, Sandrock had considerable influence over which drug programs Biogen prioritized and, over the years, proved skilled at identifying ones that would be impactful both for patients and the business.
For example, Biogen credits Sandrock for Tysabri and Tecfidera, two multiple sclerosis medications that achieved billions of dollars in sales since coming to market. Last year alone, Tysabri and Tecfidera accounted for more than half of the nearly $10.7 billion in net product revenue Biogen recorded.
Sandrock was also integral to the development of Plegridy, another multiple sclerosis drug, as well as Spinraza, the first ever medicine approved by the Food and Drug Administration to treat a rare and debilitating muscle disease known as spinal muscular atrophy.
Sandrock plans to stay on through the end of the year to help make the transition process go smoothly. In his letter, he wrote "I bleed Biogen," and that he will be cheering the company on from the sidelines moving forward.
"I leave with my head held high, proud of being from Biogen and what we have accomplished by following the science to do what is best for patients," Sandrock wrote to his colleagues.
Yet, without its go-to talent for picking the next big medicine, Biogen may have more trouble instilling investor confidence in its slate of drug programs, many of which are considered "high risk" by Wall Street analysts. In the last year or so, Biogen has discontinued a handful programs, targeting diseases ranging from multiple sclerosis and spinal muscular atrophy to Parkinson's and Alzheimer's.