On May 25, 2011, the U.S. Court of Appeals for the Federal Circuit issued an en banc decision in Therasense v. Becton Dickenson, No. 2008-1511 (Fed. Cir., May 25, 2011), outlining a heightened standard for inequitable conduct in patent infringement cases, requiring a finding of both specific intent to deceive and a “but-for” materiality.

The doctrine of inequitable conduct is a defense to patent infringement that, if proved, bars enforcement of the patent. In making its decision, the Federal Circuit noted that the doctrine evolved from three early U.S. Supreme Court Cases, which involved particularly egregious misconduct, including perjury, the manufacture of false evidence, and the suppression of evidence, to a broader scope of misconduct including the mere nondisclosure of information to the PTO. In addition, the doctrine evolved from a mere dismissal of the suit, to the unenforceability of the entire patent and its continuations and divisionals. In order to prove inequitable conduct, the accused infringer must prove intent and materiality by clear and convincing evidence. If the infringer meets this burden, the court must then weigh the equities to determine whether the applicant’s conduct before the PTO warrants rendering the entire patent unenforceable. The Federal Circuit noted that the standards for materiality have fluctuated over time, and the standard has been weakened by placing intent and materiality on a sliding scale, thus both conflating and diluting the standards at the same time. As a result, inequitable conduct has become a significant litigation strategy, increasing the complexity, duration, and cost of patent litigation. According to the Federal Circuit, one study estimated that eighty percent of patent infringement cases included allegations of inequitable conduct. This has plagued the courts and the whole patent system.

In this en banc decision, the Federal Circuit adopted a much more restrictive test for inequitable conduct. With regard to intent, an accused infringer must now prove that the patentee acted with specific intent to deceive the PTO. For example, the accused infringer must prove by clear and convincing evidence that: 

(1) the applicant knew of the reference,

(2) knew that it was material to the prosecution of the application, and 

(3) made a deliberate decision to withhold it. 

With regard to materiality, the Federal Circuit adopted a “but-for” standard, e.g. but-for the non-disclosure of the reference, the patent would not have issued.This is a much more restrictive standard than the prior standard and even the patent office’s own standard under Rule 56. In fact, the Federal Circuit said specifically that they do not adopt the PTO’s definition of materiality under Rule 56.

The Therasense decision has strictly limited the usefulness of the inequitable conduct doctrine as a defense to patent infringement. It is likely that this decision will help to simplify patent infringement cases and may lead to more patents being upheld and infringed.