Assignor Estoppel Does Not Preclude Reliance on Invalidity Decision

| Hans L. Mayer


Before Wallach, Clevenger, and Stoll. Appeals from the United States District Court District of Delaware.

Summary: The doctrine of assignor estoppel precludes an assignor from challenging the validity of a patent in district court, but not at the Patent Office.

Hologic, sued Minerva Surgical for infringement of U.S. Patent Nos. 6,872,183 (“the ’183 patent”) and 9,095,348 (“the ’348 patent”). Both patents list Minerva founder, Truckai, as an inventor.

Prior to founding Minerva, Truckai assigned his interest in two applications from which the ‘348 and ‘183 patents claim priority, and all continuation applications, to NovaCept. NovaCept was acquired by Cytyc, which was later acquired by Hologic (the current assignee of the ‘348 and ‘183 patents). Truckai and Minerva then developed a competing device.

Hologic sued Minerva alleging infringement of the ‘348 and ‘183 patents. Hologic moved for summary judgment on the issue of patent validity on the grounds that the doctrine of assignor estoppel bars Minerva from challenging the validity of the ‘348 and ‘183 patents in district court. The district court granted Hologic’s motion for both patents. Hologic moved for a permanent injunction with respect to the ‘183 patent (the ‘348 patent expired).

In parallel, Minerva requested inter partes review (“IPR”) challenging the patentability the ‘348 and ‘183 patents. The PTAB denied institution of the ‘348 patent and instituted and invalidated the ‘183 patent. Hologic appealed the PTAB’s decision and the Federal Circuit affirmed. The district court then denied Hologic’s motion for permanent injunction as moot in light of the Federal Circuit’s affirmance of invalidity. Hologic argued that assignor estoppel precludes Minerva from relying on the Federal Circuit’s holding of invalidity. The district court disagreed. Both parties appealed.

The Federal Circuit affirmed the district court’s holding that assignor estoppel precluded Minerva from challenging the validity of the ‘348 patent in district court. The Federal Circuit also affirmed the district court’s decision that Hologic is collaterally estopped from asserting infringement of the ‘183 patent because it was found invalid at the PTAB. The Federal Circuit noted the “seeming unfairness” that Minerva would have been estopped from challenging the validity of the ‘183 patent in district court but could still do so in an IPR proceeding. However, under the AIA and existing precedent, the Federal Circuit noted that Minerva was within its rights.

Justice Stoll provided further comments regarding the situation where an assignor can circumvent the doctrine of assignor estoppel by attacking the validity of a patent in the Patent Office, but cannot do the same in district court. Justice Stoll suggested that the Federal Circuit consider en banc the doctrine of assignor estoppel as it applies both in district court and the Patent Office.

Editor: Paul Stewart