Minerva Surgical, Inc. v. Hologic, Inc.

Minerva Surgical v. Hologic, decided June 29th, 2021. By a vote of five to four, in an opinion by Justice Kagan, the Supreme Court vacated the Federal Circuit and held that assignor estoppel — the rule barring a patent's assignor from later challenging its validity — remains good law, but reaches only as far as its equitable premise. It applies when, but only when, the assignor's invalidity contention contradicts a representation, explicit or implicit, made in assigning the patent. Here's the brief.

In the late 1990s, Csaba Truckai invented a device to treat abnormal uterine bleeding — the NovaSure System, which uses a moisture-permeable applicator head to destroy targeted cells in the uterine lining. He filed a patent application and assigned it, along with any future continuation applications, to his company, Novacept. That portfolio was later acquired, and the rights ended up with Hologic, which sells the device today.

Truckai kept inventing. In 2008 he founded Minerva Surgical, where he developed a competing device — the Minerva Endometrial Ablation System — using a moisture-impermeable head. Meanwhile, in 2013, Hologic filed a continuation application on the NovaSure patent and, aware of Truckai's new device, drafted a claim broad enough to cover applicator heads generally, without regard to moisture permeability. The PTO issued the amended patent in 2015.

Hologic sued Minerva for infringement. Minerva argued the newly broadened claim was invalid because it did not match the patent's written description. Hologic invoked assignor estoppel: because Truckai had assigned the original application, he and Minerva could not impeach the patent's validity. The District Court agreed, and the Federal Circuit affirmed in relevant part — deeming it irrelevant whether Hologic had broadened the assigned claims. Minerva asked the Court to abandon or narrow the doctrine.

The question was whether to discard assignor estoppel, and if not, how far it reaches.

Minerva's lead statutory argument leaned on section 282(b), which makes invalidity a defense in any action involving infringement — language it read as leaving no room for the doctrine. The Court disagreed. Assignor estoppel, it explained, traces to late-eighteenth-century England and was first approved by this Court in 1924, in Westinghouse v. Formica. It rests on a principle of fair dealing: one who assigns a patent for value implicitly represents that the patent is valid, and cannot then, to the assignee's detriment, deny what he sold. Similar defense language sat in the patent statute when Westinghouse was decided, and reading section 282(b) to abrogate the doctrine would sweep away a host of common-law preclusion rules Congress legislated against.

The Court reaffirmed the doctrine but confined it to that rationale.

The unfairness, the Court reasoned, lies in contradiction.

But the same premise marks the doctrine's limits. Where the assignor made no representation inconsistent with his later invalidity defense, there is no unfairness — and no estoppel. The Court identified three such situations.

First, where the assignment precedes any warranty of validity — as when an employee assigns rights in future, not-yet-existing inventions. Second, where a later change in law renders the original warranty irrelevant. Third, and most relevant here, where the assignee returns to the PTO after the assignment and obtains new claims broader than those assigned; the assignor never warranted those broader claims, so no inconsistency arises. Because the Federal Circuit had deemed that disparity irrelevant, the Court vacated and remanded for it to decide whether Hologic's new claim is materially broader than what Truckai assigned.

Two Justices dissented separately. Justice Barrett, joined by Justices Thomas and Gorsuch, would have discarded assignor estoppel outright, finding that the Patent Act of 1952 neither ratified Westinghouse nor left the doctrine standing as background law. Justice Alito dissented on a different ground: he thought the Court could not resolve the question without deciding whether Westinghouse should be overruled, and would have dismissed the writ.

Minerva neither created assignor estoppel nor abolished it. It reoriented the doctrine around the equitable principle the Court had recognized from the start: consistency in dealing. After Minerva, an assignor is barred from raising an invalidity defense only where that defense contradicts a representation made in the assignment. The recurring case the Court flagged — an assignee enlarging claims beyond what was assigned — falls outside the bar, leaving assignors more room to contest validity than the Federal Circuit had allowed.

Minerva Surgical, Inc. v. Hologic, Inc., 594 U.S. 559, decided June 29th, 2021. I'm John Goodhue. Thanks for watching.