On June 29, 2021, the U.S. Supreme Court decided Minerva Surgical, Inc. v. Hologic, Inc., holding that the assignor of a patent is generally estopped from later challenging its validity, but that this estoppel does not apply to grounds for invalidity that arose after the assignment.
In 2001, Csaba Truckai and his company Novacept obtained a patent on a medical device he had invented for the treatment of abnormal uterine bleeding. In 2004, Novacept sold the patent, and in the following years, Truckai invented a new device that uses a somewhat different method to treat the same condition, and began marketing it through his new company, Minerva Surgical, Inc. In the meantime, however, the holder of the 2001 patent — Hologic, Inc. — had obtained an amendment to the patent, adding claims that had not been present when Truckai sold it. Hologic sued Minerva Surgical, claiming that Truckai’s new device infringed the patent he had sold.
In response, Minerva Surgical argued (among other things) that it was not infringing the original 2001 patent, and that Hologic’s later amendment of the patent was invalid. The Federal Circuit rejected this defense, applying the doctrine of “assignor estoppel” to hold that, because Truckai had sold the patent, he and his company was estopped from now asserting its invalidity. The Federal Circuit acknowledged that Truckai was challenging the validity not of the original patent but only of a post-sale amendment, but held that estoppel still applied.
The Supreme Court vacated that decision by a 5–4 vote. The Court first rejected Minerva Surgical’s argument that the doctrine of assignor estoppel should be entirely overruled. The Court explained that a patent seller “makes an (at least) implicit representation to the buyer that the patent at issue is valid,” and that “in later raising an invalidity defense, the assignor disavows that implied warranty.” “That course of conduct,” said the Court, “strikes us, as it has struck courts for many a year, as unfair dealing—enough to outweigh any loss to the public from leaving an invalidity defense to someone other than the assignor.”
However, the Court added, “the limits of the assignor’s estoppel go only so far as, and not beyond, what he represented in assigning the patent application.” Therefore, the assignor is not estopped from asserting grounds for invalidity that arose after the assignment. For instance, when “an employee assigns to his employer patent rights in any future inventions he develops during his employment,” that does not warrant the validity of whatever patents the employer might ultimately obtain. Or if the governing law changes after the sale of a patent, “so that previously valid patents become invalid,” the seller is not estopped from asserting the new legal rule as a basis for invalidity. Or — as in this case — a patent seller is not estopped from asserting the invalidity of a post-assignment “change in patent claims.” As the Court explained, “if Hologic’s new claim is materially broader than the ones Truckai assigned, then Truckai could not have warranted its validity in making the assignment,” so “there is no basis for estoppel.”
The Court therefore vacated the Federal Circuit’s judgment, and remanded for the Court of Appeals to consider the merits of Minerva Surgical’s defense.
Justice Kagan delivered the opinion of the Court, in which Chief Justice Roberts and Justices Breyer, Sotomayor, and Kavanaugh joined. Justice Alito filed a dissenting opinion. Justice Barrett filed a dissenting opinion, joined by Justices Thomas and Gorsuch.