Cell Therapeutics will take over US sales, marketing, and development of Zevalin; Bayer Schering will continue to sell the drug outside the country.
Zevalin posted US sales of $15.4 million last year as a treatment for patients with relapsed non-Hodgkin's lymphoma.
Cell Therapeutics hopes to expand the drug's use to serve an initial treatment for non-Hodgkin's lymphoma.
"We see potential for substantial revenue growth for this product," said its chief executive, James Bianco.
Upon terms of the agreement, Cell Therapeutics will pay Biogen $10 million in cash and up to $20 million in milestone payments when the product receives approval for an additional use.