Minerva Surgical, Inc. v. Hologic, Inc.

This case, decided on June 29, 2021, by the U.S. Supreme Court, involved a patent dispute over endometrial ablation devices. The plaintiff, Minerva Surgical, Inc., sought to challenge the validity of a patent it was accused of infringing, a patent originally invented by its founder and later assigned to the defendant, Hologic, Inc. The district court barred Minerva's challenge based on the doctrine of assignor estoppel. The Supreme Court agreed to hear the case to determine if this doctrine remained valid. In a 5-4 decision, the Court upheld the doctrine of assignor estoppel but significantly narrowed its scope, ruling that it does not apply when the assignor's invalidity claim is based on developments in patent law that occurred after the assignment. The case was remanded for further proceedings consistent with this new limitation.

The U.S. Supreme Court affirmed the doctrine of assignor estoppel but narrowed its application. The Court ruled 5-4 that the doctrine is not absolute and does not bar an invalidity defense when the assignor's claim relies on legal developments occurring after the patent assignment. The lower court's decision was vacated, and the case was remanded for reconsideration under this new standard.

The central dispute focused on the continued validity and scope of the patent-law doctrine of assignor estoppel, which prevents the seller of a patent from later arguing the patent is invalid in an infringement suit. The question was whether this equitable doctrine should be abolished or limited, particularly when the defense relies on a change in patent law that post-dates the original assignment.

The ruling preserved a long-standing patent law doctrine but introduced a significant modern limitation, striking a balance between honoring contractual assignments and ensuring invalid patents are not enforced due to subsequent legal changes. It provided clarity for inventors and companies in technology transactions, particularly in the medical device sector, by defining the circumstances under which an inventor can challenge their previously owned patent.