"A reset year" is what Biogen executives called 2021 on the company’s fourth-quarter earnings call today. But, with the company’s multiple sclerosis fumarate business falling 45% in the fourth quarter and 12% over the whole year because of the entry of several generic forms of Tecfidera in the US, the group’s near-term future hinges on aducanumab gaining approval in June. Biogen claimed a positive read across from Lilly’s donanemab, the Alzheimer's project that showed promising early data last month, with further results expected at the AD/PD conference in March. If adu is approved Biogen expects to spend roughly $600m to support its launch, $200 million of which would be reimbursable by Eisai, but only modest revenues are expected in 2021 owing to the dose titration schedule needed. Biogen’s disappointing 2021 guidance caused shares to fall 3% this morning – and these forecasts assume that adu gets the green light. If it does not the outlook will be even bleaker.