Minerva Surgical v. Hologic

A defendant in a patent infringement action who assigned the patent can be barred under the doctrine of assignor estoppel from asserting a defense of invalidity if, and only if, the assignor’s claim of invalidity contradicts explicit or implicit representations the assignor made in assigning the patent. Justice Elena Kagan authored the 5-4 majority opinion of the Court. The doctrine of assignor estoppel dates back to late 18th-century England, and the U.S. Supreme Court first recognized and approved it in American jurisprudence in Westinghouse Electric & Manufacturing Co. v. Formica Insulation Co., 266 U.S. 342 (1924). The doctrine is grounded in a principle of fairness, that an inventor should not be able to assert invalidity of a patent he assigned but can merely argue about how to construe the patent’s claims. The Court refused to abandon the doctrine of assignor estoppel entirely, finding that doing so would have broad effects that contradict many of the Court’s precedents. Moreover, the principle of fairness that originally grounded the doctrine applies equally still. Specifically, when an inventor warrants that a patent claim is valid and then assigns it to another, his denial of the validity violates norms of equitable dealing. However, to fully serve that purpose of fairness, the doctrine has its limits. If the assignor did not make explicit or implicit representations that conflict with the invalidity defense, there is no ground for applying assignor estoppel. In this case, the Federal Circuit erred by not considering whether Hologic’s new claim was materially broader than the ones Truckai had assigned, which would mean that Truckai could not have warranted its validity when making the assignment. Justice Samuel Alito authored a dissenting opinion, arguing that the majority avoids answering the essential threshold question whether Westinghouse should be overruled and thus cannot answer the question presented in the petition in this case. Justice Alito would therefore dismiss the writ as improvidently granted. Justice Amy Coney Barrett authored a dissenting opinion, in which Justices Clarence Thomas and Neil Gorsuch joined, arguing that the majority recrafted a rule of assignor estoppel entirely different from that in Westinghouse. Because the Patent Act of 1952 does not incorporate the doctrine of assignor estoppel, Justice Barrett would hold the doctrine no longer applies.