Biogen has agreed to pay $1.25 billion to Danish biotech company Forward Pharma to settle part of a patent dispute over the Cambridge, Massachusetts–based drugmaker's top-selling multiple sclerosis drug Tecfidera (dimethyl fumarate). The deal will give Biogen co-exclusive licensing rights in the US and exclusive worldwide rights to the intellectual property related to the active ingredient, dimethyl fumarate. It does not, however, resolve existing patent litigation between the two companies regarding the use of dimethyl fumarate to treat multiple sclerosis (MS). Forward Pharma, which is using dimethyl fumarate to develop its own drug, challenged a Biogen patent on the ingredient, claiming it owns an earlier patent. Forward has filed an interference proceeding—which arises when two or more pending patents contain claims covering the same invention—with the US Patent and Trademark Office and a separate opposition proceeding with the European Patent Office. If Forward's patent claims prevail, it could receive annual royalties of up to 20% on Biogen's sales of Tecfidera. The MS drug generated $3.6 billion for Biogen in 2015. Biogen CEO Michel Vounatsos, eager to end the long-running litigation involving Tecfidera and move the company forward, said in a statement that the deal with Forward “will clarify and strengthen our intellectual property for Tecfidera.” In December Biogen and its partner Ionis Pharmaceuticals won US Food and Drug Administration approval for the first spinal muscular atrophy treatment (Nat. Biotechnol. 35, 99–100, 2017).