Last week, the U.S. Supreme Court issued an opinion in Minerva Surgical, Inc. v. Hologic, Inc., No. 20-440 (June 29, 2021), upholding the doctrine of assignor estoppel, but providing clarification as to its scope.
In the late 1990s, Csaba Truckai invented a device to treat abnormal uterine bleeding—the NovaSure System. Truckai filed a patent application on the invention, specifically claiming a device with a moisture-permeable head. Through a series of assignments, Hologic acquired the rights to the patent and to any future continuation applications. In 2008, Truckai founded Minerva Surgical and developed a new, moisture-impermeable device to treat abnormal uterine bleeding. Aware of this new device, Hologic filed a continuation application to add claims to the NovaSure System patent family covering all applicator heads, regardless of whether they are moisture permeable or not. After the continuation patent issued, Hologic sued Minerva for patent infringement. In defense, Minerva asserted that the continuation patent was invalid for lack of written description. The district court concluded that assignor estoppel barred Minerva from raising invalidity as a defense and ruled that Minerva infringed Hologic’s patent. The Federal Circuit affirmed. The Supreme Court granted certiorari to review the application of assignor estoppel to bar Minerva’s invalidity defense.
Generally, assignor estoppel prevents those who assign their patent rights from later contesting the validity of said patents. The doctrine is grounded in principles of fair dealing: the assignor represents—at least implicitly—that the assigned patent is valid, so it would be unfair to allow the assignor to later challenge the patent’s validity.
On review, the Supreme Court confirmed the continued viability of the assignor estoppel doctrine, but the Court also held that there are limits to its application. Specifically, the Court explained that “when the assignor has made neither explicit nor implicit representations in conflict with an invalidity defense, then there is no unfairness in its assertion” and assignor estoppel does not apply. The Court identified three examples of such a situation: (1) where the assignment occurs before an inventor can represent that specific patent claims are valid, (2) where there is a change in the law after assignment, or (3) where the patent claims are materially broadened as compared to the claims that were assigned. The Court remanded the case for a determination of whether Hologic’s continuation claims are materially broader than those originally assigned by Truckai.
This blog post was co-authored by Heather Kliebenstein and Andrew Nemecek