New Limits Set For Assignor Estoppel – A Look Into The Case That Defined Them

Under patent law, there are court-created doctrines under which one cannot properly challenge the validity of a patent.  One such doctrine is Assignor Estoppel, whereby someone who previously owned a patent, such as an inventor, and assigned it to another party cannot challenge the validity of that patent. In a recent Supreme Court case, Minerva Surgical, Inc. v. Hologic, Inc. et. al. (decided June 29, 2021) the Supreme Court defined limits on Assignor Estoppel.

In the case, inventor Truckai invented a device to treat uterine bleeding and assigned the later granted patent and its later possible applications to a company that was subsequently sold to Hologic, Inc.  The patent‘s specification described portions of the device only in a general way. Truckai later asserted that he invented an improvement to the device using a moisture-permeable applicator head (which apparently was not explicitly disclosed in the first patent). He filed a new patent application narrowed from the earlier application at least in part by adding descriptive material absent from the original disclosure.  That application was ultimately issued, and Truckai assigned it to Minerva.  Hologic also filed a new continuation application based on the original specification, which issued with new claims and may have included an applicator head.  Hologic brought a suit for invalidity and infringement against Minerva relative to their newer patent arguing for Assignor Estoppel.

The Supreme Court’s majority opinion relies on precedent and on a general doctrine of fairness.  Finding in favor of Minerva, the Supreme Court remanded to the Court of Appeals for the Federal Circuit (“CAFC”) to determine whether the claims in the Minerva patent should be invalidated based on adequate disclosure in the later Hologic patent, or whether Hologic’s claims went beyond the original disclosure (essentially invalidating the Hologic patent).

As a guidepost in this case, the Supreme Court said that an assignment alone is insufficient for Assignor Estoppel to apply.  Relying on fairness, the Court held that the specification of the assigned patent must disclose the later claims.  The Court said that “[i]f Hologic’s new claim is materially broader than the ones Truckai (originally) assigned, then Truckai could not have warranted its validity in making the assignment”.  In other words, the Court is limiting the first assignment to only that described in the specification and not more.  In this case, it may well be that the claims of the Minerva patent were not disclosed in the Hologic patent.  The CAFC will decide.

This case highlights the importance of being as complete as possible in a patent application’s disclosure.  While it may well be that Truckai’s later invention could not even be envisioned at the time of the earlier filing, any reasonably possible options should be included in an original disclosure.  Hologic clearly tried and succeeded at patenting additional claims, which could ultimately render the later Minerva patent invalid, or Hologic’s patent might be rendered invalid, but again, it all depends on what was disclosed in the first filing.