Background
Csaba Truckai invented a device for endometrial ablation (the NovaSure system) and assigned his patent rights to NovaCept, which was later acquired by Hologic, Inc. Truckai then founded Minerva Surgical and developed a competing endometrial ablation product (the Minerva Endometrial Ablation System). Hologic sued Minerva for infringement of patents that covered the technology Truckai had originally assigned.
Minerva defended on multiple fronts: it challenged the patents’ validity in district court and also filed inter partes review (IPR) petitions at the PTAB seeking to invalidate the patents. The key legal issue was whether the doctrine of assignor estoppel — which generally prevents a patent assignor from later arguing the assigned patent is invalid — applied to (1) Minerva’s invalidity defense in district court, and (2) Minerva’s IPR petitions at the PTAB. Hologic argued that assignor estoppel should bar Minerva’s challenges in both forums.
The Court’s Holding
The Federal Circuit held that assignor estoppel barred Minerva from raising invalidity arguments in district court, but did not bar Minerva from filing IPR petitions at the PTAB. The court reasoned that the two forums operate under different legal frameworks. In district court, assignor estoppel is a well-established equitable doctrine that prevents an assignor from denying the validity of the patent rights it assigned — because it would be unfair and inequitable for an assignor to take money for the rights and then turn around and argue those rights are worthless.
The IPR context is different, the court held, because IPR is a creature of statute — the America Invents Act (AIA) — and the AIA broadly allows “any person” (with limited exceptions) to file IPR petitions. The court found no basis in the AIA text for grafting the common-law equitable doctrine of assignor estoppel onto the PTAB’s statutory framework. Congress did not include assignors among the categories of persons barred from filing IPR petitions, so courts cannot impose that restriction through equitable doctrines.
This case was later reviewed by the Supreme Court (in Minerva Surgical, Inc. v. Hologic, Inc., 2021), which affirmed that assignor estoppel survives but narrowed its scope to situations where the assignor’s later invalidity argument directly contradicts representations the assignor made in obtaining or assigning the patent.
Key Takeaways
- Assignor estoppel bars a patent assignor from challenging the validity of the assigned patent in district court, even if the assignor later develops competing products covered by the patent.
- Assignor estoppel does not bar an assignor from filing IPR petitions at the PTAB — the AIA’s “any person” standing for IPR petitions overrides the equitable doctrine in the PTAB forum.
- A patent assignor facing infringement claims can still challenge validity at the PTAB through IPR, even if it cannot raise the same invalidity defenses in the concurrent district court case.
- Companies acquiring patent rights through assignment should be aware that the assignor retains IPR petition rights, creating a potential asymmetric challenge: the assignee can sue in district court while the assignor simultaneously attacks validity at the PTAB.
Why It Matters
The 2020 Hologic v. Minerva decision created a significant and somewhat counterintuitive asymmetry in post-grant patent challenges. An inventor who assigns away patent rights and later starts a competing company cannot argue invalidity in district court — but can still petition the PTAB to invalidate the same patent through IPR. This means that in parallel proceedings, the assignor-turned-infringer could be estopped from invalidity defenses in district court while simultaneously succeeding in an IPR that invalidates the patent.
For patent assignees and acquirers, this underscores the importance of including IPR waiver provisions in patent assignment agreements — provisions that contractually bind the assignor not to file IPR petitions, even though the law does not bar such filings absent such a contract. The Federal Circuit’s later decision in Nippon Shinyaku v. Sarepta (2022) confirmed that such IPR waiver agreements are enforceable, providing assignees with a tool to close the gap that this Hologic v. Minerva decision exposed.