In Minerva Surgical, Inc. v. Hologic, Inc. (June 29, 2021), the Supreme Court upheld, but narrowed, the doctrine of assignor estoppel, which typically bars a patent assignor from later arguing its assigned patent is invalid in defense to the assignee’s infringement claim against the assignor.
The patent in this case, asserted by Hologic against Minerva, was a medical device patent that issued as a continuation patent from a patent portfolio Hologic acquired from Novacept. The inventor, Csaba Truckai, previously assigned his rights to the underlying patent application to Novacept, but then founded a new company, Minerva. Hologic then sued Minerva for infringing a later-issued continuation patent. The lower courts held that Minerva was barred by assignor estoppel from challenging the validity of Hologic’s continuation patent.
In a 5-4 decision, the Supreme Court upheld the viability of the doctrine of assignor estoppel, recognizing its importance and common-law origins grounded in consistency and fairness in dealing with others. Justice Kagan then explained, however, that assignor estoppel applies only when “the assignor’s claim of invalidity contradicts explicit or implicit representations he made in assigning the patent.”
One noncontradictory example provided by the Court is when a change is made to the scope of patent claims after a patent is assigned. Namely, if a later obtained patent issues with claims that are “materially broader” than the claims at the time of assignment, the assignor could not have warranted the new claims’ validity and assignor estoppel would not apply. This was the issue in Minerva, and the Supreme Court vacated and remanded the case to the Federal Circuit to determine whether Hologic’s new claim was materially broader than the claims Truckai had assigned.
The Court’s holding leaves in place the equitable doctrine of assignor estoppel but allows for narrow instances in which an assignor is still able challenge a patent’s validity.
The Court’s decision is accessible at: https://www.supremecourt.gov/opinions/20pdf/20-440_9ol1.pdf.
Lerner David has successfully represented its clients in patent infringement actions involving continuation patents for over 50 years and is highly experienced in cases involving equitable defenses such as assignor estoppel.