In Regeneron Pharmaceuticals, Inc. v. Merus N.V., No. 2016-1346, slip op. (Fed. Cir. July 27, 2017) (hereafter, “Slip Op.”), the Federal Circuit seems to have loosened the standards for finding a patentee culpable of inequitable conduct during patent prosecution. By affirming the district court’s finding of inequitable conduct, the court in Regeneron condones the use of circumstantial evidence arising during litigation to infer that the patentee had specific intent to deceive the Patent and Trademark Office (PTO) during prosecution. The opinion was authored by Chief Judge Prost and joined by Judge Wallach. Judge Newman dissented.

Inequitable Conduct

“Inequitable conduct is an equitable defense to patent infringement that, if proved, bars enforcement of a patent.” Therasense, Inc. v. Becton, Dickinson & Co., 649 F.3d 1276, 1285 (Fed. Cir. 2011). To show that an applicant engaged in inequitable conduct before the PTO, a party must show by clear and convincing evidence that “the applicant misrepresented or omitted material information with the specific intent to deceive the PTO.” Id. at 1287. This analysis requires a showing of both materiality of the misrepresentation and intent to deceive. Id. The defense is most often wielded as an assertion by the accused infringer that the patent applicant knowingly withheld a material prior art reference from the PTO during prosecution.