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Can Patent Assignors Challenge Patent Validity? U.S. Supreme Court to Decide



On Friday, January 8, 2021, the U.S. Supreme Court granted a writ of certiorari filed by Minerva Surgical Inc. in a dispute with Hologic Inc. The question presented by Minerva is “whether a defendant in a patent infringement action who assigned the patent, or is in privity with an assignor of the patent, may have a defense of invalidity heard on the merits.” The U.S. Supreme Court took no action on a cross-petition from Hologic, which argued that assignor estoppel should apply not only in district court, but also in inter partes reviews at the Patent Trial and Appeal Board (PTAB).

Under the doctrine of assignor estoppel, a patent seller is prevented from assigning a patent to another and then attacking the validity of that patent in a subsequent patent infringement litigation. Minerva argues that “Assignor estoppel singles out a class of individuals – inventors, who are likely well positioned to expose a patent’s flaws or highlight the way an assignee has asserted a patent beyond its legitimate scope – and bars them from challenging validity.”

Hologic sued Minerva in 2015 in the District Court of Delaware over two patents, U.S. Patent No. 6,872,183 (“the ‘183 patent”) and U.S. Patent No. 9,095,348 (“the ‘348 patent”) on devices and procedures for endometrial ablation. Csaba Truckai is named as an inventor on both patents and the patents are assigned to a company that was later acquired by Hologic. Truckai later founded Minerva and obtained a patent on a new device. Minerva disclosed the new device to Hologic, but instead of investing in Minerva’s new device, Hologic filed a continuation application of the ‘183 patent application to expand the scope of the patent claims, which ultimately issued as the ‘348 patent. Hologic then sued Minerva for infringement of the ‘183 patent and the ‘348 patent.

Minerva asserted that the ‘348 patent was invalid for lack of enablement and lack of written description. Hologic responded that Minerva was prevented from arguing the invalidity of the ‘348 patent due to assignor estoppel. The district court ruled, and the Federal Circuit affirmed, in favor of Hologic that Minerva was prevented from asserting any invalidity defenses due to assignor estoppel.

Minerva, however, argues that the rational for the assignor doctrine was to prevent assignors from later asserting that what they had assigned was worthless. Minerva states that they never asserted that was assigned was worthless, but that the later filed ‘348 patent has unsupported expansion of the scope of the claims in the patent, and that Minerva should be able to challenge the validity of the ‘348 patent for lack of enablement and written description. Hologic has taken the opposite position and says that assignor estoppel should be affirmed and that assignor estoppel should also apply at the PTAB.

The U.S. Supreme Court will decide whether they agree with Minerva that assignor estoppel, at least in some situations, undermines patent law’s public purposes by barring a way to challenge the validity of patents.