Runaway Jurisprudence: Has the “But For” Test for Proving Inequitable Conduct in Patent Cases Gone Awry, Gone Rogue, or Gone Quiet?

This article originally appeared in Vol. 40, No. 2 of New Matter, the publication of the IP Section of The State Bar of California. Any opinions in this article are not those of Winston & Strawn or its clients. The opinions in this article are the author’s opinions only.

On May 25, 2011, the Federal Circuit set forth in its en banc Therasense opinion a new, heightened test requiring that a prior art reference, knowingly withheld by the applicant, be “but for” material to the patent’s issuance in order to constitute inequitable conduct that would render the obtained patent unenforceable. On January 8, 2015, the Federal Circuit denied the combined petition for panel rehearing and for rehearing en banc in its decision in American Calcar, Inc. v. American Honda Motor Co., Inc. (hereinafter “American Calcar II”). The inequitable conduct claims at issue had been evaluated previously by the court in June of 2011 (hereinafter “American Calcar I”), on the heels of the Therasense decision, and had been remanded to the district court for more detailed determinations of materiality and intent. With the original Therasense majority currently occupying merely a third of the seats and with Judge Prost, a member of the dissent, assuming the duties of chief judge, does American Calcar II break rank with post-Therasense precedent – including American Calcar I – and offer any clues as to what direction the court may be headed?