Biogen agreed to acquire Apellis Pharmaceuticals for approximately $5.6 billion, expanding its portfolio in immunology and rare-disease treatments. Under the deal, disclosed Tuesday, Biogen will pay $41 per share in cash plus a $2-per-share contingent value right tied to Syfovre sales targets.

The acquisition adds two commercialized medicines to Biogen's lineup: Syfovre for geographic atrophy and Empaveli for rare immune-mediated kidney diseases. These therapies generated $689 million in combined net sales in 2025, immediately boosting Biogen's revenue stream.

Biogen stated the acquisition enhances both short and long-term revenue growth, with the drugs expected to expand at a mid-to-high teens rate through at least 2028. The deal positions Biogen to strengthen its position in the rare disease treatment market with two differentiated medicines already generating substantial revenue.