§ I. Patent Cases
I.a. Supreme Court decisions
Minerva Surgical, Inc. v. Hologic, Inc., 141 S. Ct. 2298 (2021)
Facts: This case concerns the conditions for applying assignor estoppel where a party who assigns its patent rights later asserts an invalidity defense to that patent.
In the late 1990s, Csaba Truckai invented a device for treating abnormal uterine bleeding using a moisture-permeable applicator head and assigned the patent application to his company Novacept. Hologic later acquired Novacept. Truckai also founded Minerva Surgical, and obtained a patent directed to an improved device to treat abnormal uterine bleeding using a moisture-impermeable applicator head. Meanwhile, Hologic filed for another patent in the same patent family as the Novacept application, and obtained a broad patent claim to applicator heads, without regard to whether they are moisture permeable.
Hologic sued Minerva for patent infringement of this newly obtained claim. In response, Minerva argued that Hologic’s patent was invalid because the new, broad claim to applicator heads did not correspond to the invention’s written description, which addressed applicator heads that were water permeable. Hologic then invoked the doctrine of assignor estoppel, arguing that Truckai and Minerva could not challenge patent validity. The District Court granted summary judgment to Hologic, holding that assignor estoppel barred Minerva’s invalidity defense, and the Court of Appeals for the Federal Circuit affirmed in relevant part. The Supreme Court granted certiorari.
Held: The doctrine of assignor estoppel is upheld, but the judgment was vacated and remanded. Assignor estoppel applies only when the assignor’s assertions of invalidity contradicts explicit or implicit representations the assignor made in assigning the patent.
Reasoning: The doctrine of assignor estoppel, which limits an inventor’s ability to assign a patent to another for value and later contend in litigation that the patent is invalid, is based on equitable principles. Assignor estoppel reflects a demand for consistency and fair dealing with others. A person should not be able to sell his or her patent rights—making an implicit representation that the patent at issue is valid—and later raise an invalidity defense, disavowing that implied warranty. But when an …