Minerva Surgical, Inc. v. Hologic, Inc.

Minerva Surgical, founded by inventor Csaba Truckai, developed an endometrial ablation device. Truckai had earlier assigned related patents to Cytyc, which was later acquired by Hologic. Hologic sued Minerva for patent infringement. Minerva sought to challenge the patents' validity, but lower courts barred that challenge under assignor estoppel. The U.S. Supreme Court held that assignor estoppel remains a valid doctrine, but it is not absolute. It does not apply when the patent claims are materially broadened after assignment or when intervening legal changes create new invalidity grounds. The Court vacated the Federal Circuit's judgment and remanded for further proceedings.

The U.S. Supreme Court vacated the Federal Circuit's judgment and remanded the case. It preserved assignor estoppel but held it does not apply when the assignor challenges claims that were broadened after assignment or when there has been a change in law making previously valid patents invalid.

Whether the equitable doctrine of assignor estoppel should bar a patent assignor from asserting invalidity as a defense in an infringement suit, and what limits should apply to that doctrine.

The ruling clarified the limits of assignor estoppel, affecting employee inventors, patent acquisitions, and innovation. It balanced fairness to assignors with the need for patent certainty, influencing how companies draft assignment agreements and how courts handle validity challenges in patent litigation.