Assignor Estoppel in Patent Law: Important Limitations Defined
Supreme Court Clarifies Assignor Estoppel Limits in Patent Cases
The Supreme Court recently issued a ruling on Minerva Surgical, Inc. v. Hologic, Inc. further defining the boundaries of a patent law doctrine, assignor estoppel. The doctrine of assignor estoppel states that an inventor who assigns the rights in their patent to a company may not later in litigation argue that the patent is invalid. In the act of assigning, the patent the inventor is making explicit or implicit warranties that the patent is valid and so to later argue the contrary, would be unfair and inequitable.
Assignor Estoppel Limits with Blanket Assignments
In their opinion, the Supreme court outlines the three scenarios where assignor estoppel may not apply, as there is no contradiction. The first is when an assignment by the inventor occurs before the inventor could possibly make a warranty of validity. The example the Supreme Court provides for this case is when an inventor signs a blanket assignment for anything they invent while working for the employer. In this case, the employer is selecting what gets patented, and so the inventor has not made any statement of validity for each specific invention. As a company, one way to address this is to have inventors sign an assignment for each patent or application they file, so the warranty of validity is present in each case.
Change in Law Limits to Assignor Estoppel
The second example offered is when a later legal development renders the warranty given invalid. In this example, the warranty given for the patent was valid when it was given. This presumes the law later changes such that a previously valid patent is now invalid. In this case the inventor is not estopped because the change in law prevents a contradiction since the patent is in fact now invalid. There is not much a business or inventor can do to plan for in this case as the scenario hinges on the law changing unfavorably.
Assignor Estoppel Limits Due to Post-Assignment Developments
The final example, and most relevant in the present case, is a post-assignment development can remove the rationale for applying assignor estoppel. In the case this arose as the inventor, Truckai, assigned a patent to the company he was working for at the time. The company later sold all of its IP rights to Hologic. The inventor then left to form Minerva Surgical (“Minerva”). At Minerva, the inventor created and patented an improved version of the device he had invented previously. Hologic filed a continuation on the original patent that would also cover the new patent. Once Hologic received the continuation, it filed suit against Minerva for infringement. The Supreme Court noted that the claims in the continuation were broader than those in the original patent. Since the claims were now significantly broader than they were previously, the claims now extended beyond the scope of the assignment and so there was no contradiction when the inventor asserted than the broader claims were invalid. The Supreme Court summarized, “[i]f Hologic’s new claim is materially broader than the ones Truckai assigned, then Truckai could not have warranted its validity in making the assignment. And without such a prior inconsistent representation, there is no basis for estoppel.”
Key Takeaways on Limits to Assignor Estoppel in Patent Law
The Supreme Court in the Minerva Surgical, Inc. v. Hologic, Inc. case reaffirmed that assignor estoppel is a doctrine that is alive in patent law, but also helped define and cement the boundaries of the doctrine with limits in:
blanket assignments;
unfavorable changes in law; and
post assignment developments.
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