In yet another appellate case with spirited dissents, the Court of Appeals for the Federal Circuit (CAFC) continues to reveal differences of opinion among members of the court in how precedent and the use of extrinsic evidence should guide current decisions. In the recent case of Biogen International GmbH v. Mylan Pharmaceuticals, which dealt with the adequacy of a patent's written description under 35 USC §112, there were strong dissents in the panel decision and in the court's denial of requests for a panel rehearing and rehearing en banc.

By way of background, Mylan filed an Abbreviated New Drug Application (ANDA) with the FDA under the Hatch-Waxman Act (the Act) to manufacture, use, and market a generic dimethyl fumarate (DMF) drug for the treatment of multiple sclerosis (MS). Biogen owned U.S. Patent 8,399,514 directed to a method of treating MS using a DMF-based drug. Biogen filed suit for patent infringement against Mylan under the Act, asserting several patents including the '514 Patent. Mylan counterclaimed seeking a declaratory judgment of invalidity.