Supreme Court Maintains But Constrains Assignor Estoppel

  • June 30, 2021


The Supreme Court’s 5-4 decision in Minerva v. Hologic, Inc., issued on June 29, 2021, reaffirmed that the judicial doctrine of assignor estoppel remains good patent law. But, the Court held that the Federal Circuit’s application of the doctrine had been too rigid, and clarified that the doctrine only applies when its underlying principle of fair dealing comes into play.

Novacept, Inc. is the owner of a patent directed to a device capable of improving the treatment of abnormal uterine bleeding. Novacept’s device, the NovaSure System, uses a “moisture permeable” applicator head to avoid burning or ablation while the device operates to remove targeted cells in the uterine lining. The FDA approved the device in 2001. In a series of sales following the FDA’s approval, Hologic, Inc. acquired Novacept’s IP assets and sold Novacept’s device across the United States.

In 2008, Csaba Truckai, founder of Novacept and inventor-assignor of the original NovaSure patent, founded Minerva Surgical Inc., and developed a device similar to the NovaSure System. But, Minerva claimed its device was distinct because its applicator head is “moisture impermeable.” The FDA approved Minerva’s device in 2015.

Meanwhile, Hologic sought a continuation application for the NovaSure System. In a strategic play, Hologic drafted a broad claim covering applicator heads without regard to moisture permeability. The PTO issued the patent from Hologic’s continuing application in 2015, and Hologic filed suit just months later alleging that Minerva’s device infringed its new patent. Minerva attempted to argue that the asserted patent was invalid because the broad new claims were not supported by the 2001 specification, which only addressed moisture-permeable applicator heads. But, Hologic objected to Minerva’s validity challenge on the basis of assignor estoppel.

The doctrine of assignor estoppel is a judicially-created doctrine intended to prevent inconsistent representations about a patent’s validity. An assignor of a patent is estopped from challenging its validity. It embodies the principle that the assignor of a patent cannot fairly attack the right he formerly sold.

Over time, the Supreme Court has clarified some of the doctrine’s limitations, while recognizing that other questions may have to be resolved at a later date. It has held that an assignor cannot later challenge the validity of a patent, but they may still use prior art to narrowly construe a claim to avoid infringement. And, while the Court had speculated that assignor-estoppel may work differently for an issued patent than for a pending application, the Court had not had the occasion to decide that issue one way or another.

Here, the District Court applied the doctrine of assignor estoppel preventing Minerva from raising an invalidity defense, and the Federal Circuit affirmed. The Supreme Court granted certiorari to consider whether the doctrine of assignor estoppel was still good law, and if the Federal Circuit had applied it correctly.

A majority of the Court, led by Justice Kagan and joined by Justices Breyer, Sotomayor, Kavanaugh and Chief Justice Roberts, declined Minvera’s request to abolish assignor estoppel altogether. The majority did not accept Minerva’s argument that Congress’s decision not to incorporate assignor estoppel into the 1952 Patent Act abrogated the doctrine, because many judicial doctrines, like res judicata, survive without being incorporated into statute. Nor did the majority agree that its other opinions had effectively abrogated the doctrine already. In particular, the Court’s decision to abolish the doctrine of licensee estoppel did not extend to the present case, because licensee estoppel could not be supported by the principle that parties should be bound by their representations in a negotiation in the same way that assignor estoppel could. And, the Court did not accept that modern policy rationales favoring the elimination of bad patents justified abolishing the doctrine, because the fundamental fairness principles supporting the doctrine remained compelling.

However, the majority did find the Federal Circuit’s application of assignor estoppel to be overly rigid, and held that the doctrine could only be applied where it implicated principles of fairness and fair dealing. That is, assignor estoppel could only bar challenges to validity that purport to undermine the assignor’s implicit or explicit warranties and representations. But, where an assignor could not reasonably make representations about the validity of an assignment, the doctrine cannot apply. For example, common employment agreements to assign future inventions to the employer would not implicate the doctrine because the employee could not make representations regarding the validity of an invention that has not come into being. Or, where the governing law changes following an assignment, the assignor can challenge the validity of a patent grounded in that change. And most importantly here, if the claims of a pending application change and broaden after it is assigned, the doctrine does not apply because the assignor could not have warranted the validity of the new claims.

The Federal Circuit had erred by holding that it was irrelevant whether the claims had been broadened after they were assigned. The Court therefore remanded the case to consider that question.

The decision included two dissents, the first by Justice Alito writing for himself, and the second by Justice Barrett writing for the remaining dissenters. Justice Barrett would have found that the 1952 Patent Act did not ratify prior precedent recognizing assignor estoppel. Justice Alito largely focuses his attacks on his fellow dissenters, but dissents himself because he would have squarely addressed whether that underlying precedent should be overruled.

The Court’s decision in Minvera extends a recent Supreme Court trend of eliminating clear but rigid Federal Circuit doctrines, in favor more nuanced and fact-specific approaches. The doctrine of assignor estoppel remains good law, but courts must consider whether to apply it in view of what, specifically, the assignor warranted or could have warranted when the assignment was made. This may greatly limit the application of the doctrine in cases concerning assignments of future inventions, such as in employment agreements, and in the assignment of pending applications where the claims are subject to change. And, other implications may still need to be explored.


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