Astrid R. Spain is a partner at McDermott Will and Emery LLP. A member of the Intellectual Property, Media and Technology Department and the Life Sciences and Medical Devices Practice Group, she is based in San Diego. Demetria A. Buncum is an associate at McDermott Will and Emery based in the Washington, D.C. office. She is a member of the Intellectual Property, Media and Technology Department. Affirming a district court ruling which had taken the relatively rare step of holding an asserted patent unenforceable due to inequitable conduct, the U.S. Court of Appeal for the Federal Circuit emphasized several categories of information that a patent prosecutor must disclose to the U.S. Patent and Trademark Office (USPTO) in order to satisfy a patent applicantââ?¬â?¢s duty of candor. McKesson Information Solutions, Inc. v. Bridge Medical, Inc., Case No. 06-1517 (Fed. Cir., May 18, 2007) (Clevenger, J.; Newman, J., dissenting). The district court found that McKessonââ?¬â?¢s patent was unenforceable due to inequitable conduct during prosecution based on failure by the patent attorney to submit three material pieces of information during prosecution of three related applications, two examined by one examiner (Trafton) and a third by a different examiner (Lev). The materials included a prior art patent that had been brought to the attorneyââ?¬â?¢s attention by Examiner Lev in a co-pending application, the rejection of claims in that same co-pending application and the allowance of another co-pending application. The first item of non-disclosed information was a prior art patent that had been brought to the patent attorneyââ?¬â?¢s attention by Examiner Lev. While the patent attorney notified Examiner Trafton of the co-pending application, the cited prior art patent was not expressly disclosed. The Court concluded that the prior art patent was material and non-cumulative as it described the relevant three-node system (relied on by applicant for patentability in the application before Examiner Trafton) in greater detail than any other reference. The Court concluded that the high materiality of the reference and lack of a credible explanation for the non-disclosure supported the conclusion that the district court did not commit clear error. In particular, the Court found that the prosecuting attorneyââ?¬â?¢s cancellation of claims directed to both a three-node communication and a unique address in response to a rejection in view of the prior art patent gave rise to an inference that he recognized the patent would present a significant obstacle to patentability in the related application. The second item of non-disclosed information was the prosecuting attorneyââ?¬â?¢s failure to inform Examiner Trafton about the grounds of rejection of substantially similar claims pending before Examiner Lev. The Court analogized the facts to those in its own precedent, Li Second Family Ltd. v. Toshiba Corp., and found significant similarities. As in Li Second Family, the examiner of one application (Trafton) was not apprised of the adverse decisions by another examiner (Lev) in a closely related application. The patent attorney failed to mention the adverse decisions in the related application, and the patent attorney also made statements to the examiner inconsistent with the other examinerââ?¬â?¢s decisions, i.e., that nothing in the prior art disclosed relevant three-node communication. The Court also rejected the argument that disclosure to Examiner Trafton of the existence of the application being examined by Examiner Lev was sufficient to discharge the attorneyââ?¬â?¢s Rule 56 duty of disclosure. Finally, the Court held that failure to disclose the allowance of a different co-pending application constituted a third instance of inequitable conduct. According to the Court, the allowance gave rise to a ââ?¬Å?conceivable double patenting rejectionââ?¬Â? and therefore should have been disclosed. The Court affirmed on this basis despite the fact that the same USPTO examiner reviewed both applications, citing the Manual of Patent Examining Procedure (MPEP) provision that counsels attorneys not to assume that an examiner remembers every detail of every file. Judge Newman dissented. In her view, there was no clear and convincing evidence of deceptive intent simply because the prosecuting attorney did not inform the examiner of a related case of common parentage or of a reference cited in the related case. ââ?¬Å?To avoid the inequity resulting from litigation driven distortion of the complex procedures of patent litigation, precedent firmly requires that the intent element ââ?¬Â¦ must be established by clear and convincing evidence of deceptive intentââ?¬â??not of mistake, if there were such, but of culpable intent.ââ?¬Â? Practice Note: This decision significantly increases the extent to which the duty of candor extends to activities occurring during prosecution of related applications. Reprinted with permission from McDermott Will and Emery’s IP Update, June 2007.