Intellectual property lawyers are hoping an upcoming en banc rehearing at the U.S. Court of Appeals for the Federal Circuit will resolve a hotly debated question about how specific patent applicants must be when describing innovations.

The rehearing of Ariad Pharmaceuticals Inc. v. Eli Lilly and Co. could reverse a written-description requirement for patents that the court itself imposed a dozen years ago. The controversy has since resurfaced several times in other Federal Circuit cases.