SCOTUS imposes new limits on assignor estoppel

Managing IP is part of Legal Benchmarking Limited, 1-2 Paris Gardens, London, SE1 8ND

Copyright © Legal Benchmarking Limited and its affiliated companies 2025

Accessibility | Terms of Use | Privacy Policy | Modern Slavery Statement

SCOTUS imposes new limits on assignor estoppel

adobestock-87599523.jpeg

In a five to four ruling, the US Supreme Court upheld the doctrine of assignor estoppel but said it could only be used in certain instances

The US Supreme Court upheld the doctrine of assignor estoppel today, June 29, but imposed new limits on when it could be used.

In a five to four decision in Minerva v Hologic, the high court ruled that while there are valid uses for the doctrine – which bars inventors from challenging their own patents today – it has been applied in the past to improperly stop warranted challenges to patent validity.

Justice Elena Kagan, who wrote the majority opinion, said the doctrine applies only when an inventor says one thing (explicitly or implicitly) in assigning a patent and the opposite in litigating against the patent’s owner.

Stefan Szpajda, partner at Dorsey & Whitney in Seattle, said: “The Supreme Court’s ruling honours the centuries-old fairness principles on which assignor estoppel is based, while acknowledging the practical contemporary reality of how patents are invented, assigned, and later sold.

“The majority’s ruling will be seen as a win for competition and employee mobility, as it will make it harder for companies to rely on assignor estoppel to shield their patents from challenge by competitors who hire their former employees.”

This issue of assignor estoppel arose in the case after Hologic, a medical devices company, sued uterine health specialist Minerva for infringing certain claims of its US patents (6,872,183 and 9,095,348). Hologic had acquired the rights indirectly from the founder of Minerva, Csaba Truckai.

Minerva asserted invalidity arguments and filed inter partes reviews at the Patent Trial and Appeal Board (PTAB), before Hologic responded by asserting assignor estoppel.

The PTAB decided that the method patent claims were invalid, and Minerva asked the District Court for the District of Delaware to dismiss the asserted claims from those patents as moot. The district court denied the request because the claims had not yet been cancelled and were still subject to appeal.

Hologic then moved for summary judgment at the district court, which granted the motion and agreed with the company that assignor estoppel barred Minerva from asserting invalidity.

After the trial, the Court of Appeals for the Federal Circuit affirmed the PTAB’s final written decision concerning the unpatentability of the method patent claims.

As a result, the district court denied Hologic's motion for a permanent injunction and for supplemental damages. Hologic and Minerva appealed to the Federal Circuit.

On appeal, the appellate court affirmed-in-part and vacated-in-part the District of Delaware's judgment, and remanded the case.

Both parties ended up appealing to SCOTUS. The high court accepted the petition for writ of certiorari from Minerva on January 8, but denied Hologic’s petition.



more from across site and SHARED ros bottom lb

More from across our site

IP is becoming one of the most significant drivers of major deals, and law firms are altering their practices to reflect the change
In the second in a new podcast series celebrating the tenth anniversary of IP Inclusive, we discuss IPause, a network set up to support those experiencing (peri)menopause
Firms are adapting litigation strategy as Brazil’s unique legal system and technical expertise have made preliminary injunctions a key tool in global patent disputes
A ruling on confidentiality by the the England and Wales Court of Appeal and an intervention from the US government in the InterDigital v Disney litigation were also among top talking points
Moore & Van Allen hires former Teva counsel Larry Rickles to help expand the firm’s life sciences capabilities
Canadian law firms should avoid ‘tunnel vision’ as exclusive survey reveals client dissatisfaction with risk management advice and value-added services
In major recent developments, the CoA ruled on director liability for patent infringement, and Nokia targeted Paramount at the UPC and in Germany
Niri Shan, the newly appointed head of IP for UK, Ireland and the Middle East, explains why the firm’s international setup has brought UPC success, and addresses German partner departures
Vlad Stanese joins our ‘Five minutes with’ series to discuss potentially precedent-setting trademark and copyright cases and his love for aviation
Heath Hoglund, president of Via LA, discusses how it sets royalty rates and its plans to build on growth in China
Gift this article