Minerva Surgical, Inc. v. Hologic, Inc.

Decision Date29 June 2021
Docket NumberNo. 20-440,20-440
Citation210 L.Ed.2d 689,141 S.Ct. 2298
Parties MINERVA SURGICAL, INC., Petitioner v. HOLOGIC, INC., et al.
CourtU.S. Supreme Court

Vera M. Elson, Wilson Sonsini Goodrich & Rosati, P.C., Palo Alto, CA, Edward G. Poplawski Olivia M. Kim, Wilson Sonsini Goodrich & Rosati, P.C., Los Angeles, CA, Robert N. Hochman, Caroline A. Wong, Sidley Austin LLP, Chicago, IL, Jillian Sheridan Stonecipher, Sidley Austin LLP, Washington, DC, for Petitioner.

Matthew M. Wolf, Counsel of Record, Jennifer A. Sklenar, Marc A. Cohn, R. Stanton Jones, William C. Perdue, Sean A. Mirski, Arnold & Porter, Kaye Scholer LLP, Washington, DC, William M. Jay, Goodwin Procter LLP, Washington, DC, David J. Zimmer, Goodwin Procter LLP, Boston, MA, for Respondent.

Justice KAGAN delivered the opinion of the Court.

In Westinghouse Elec. & Mfg. Co. v. Formica Insulation Co. , 266 U.S. 342, 349, 45 S.Ct. 117, 69 L.Ed. 316 (1924), this Court approved the "well settled" patent-law doctrine of "assignor estoppel." That doctrine, rooted in an idea of fair dealing, limits an inventor's ability to assign a patent to another for value and later contend in litigation that the patent is invalid. The question presented here is whether to discard this century-old form of estoppel. Continuing to see value in the doctrine, we decline to do so. But in upholding assignor estoppel, we clarify that it reaches only so far as the equitable principle long understood to lie at its core. The doctrine applies when, but only when, the assignor's claim of invalidity contradicts explicit or implicit representations he made in assigning the patent.


Inventors look to the patent system to obtain valuable rights. A typical patent application, filed with the U.S. Patent and Trademark Office (PTO), includes a written description and drawing of the invention and one or more claims particularly setting out the invention's scope. See 35 U.S.C. §§ 111 – 113. The application also usually contains an inventor's oath—a statement attesting that the applicant is "the original inventor" of the "claimed invention," so that he is entitled to the patent sought. § 115. If the PTO decides that the invention meets the "conditions for patentability"—mainly, that the invention is useful, novel, and non-obvious—it will issue a patent to the inventor. See §§ 101–103. That award gives the inventor the right to exclude others from making, using, or selling the invention until the patent expires (currently, 20 years after the application date). See § 154.

The invention sparking this lawsuit is a device to treat abnormal uterine bleeding, a medical condition affecting many millions of women. Csaba Truckai, a founder of the company Novacept, Inc., invented the device—called the NovaSure System—in the late 1990s. He soon afterward filed a patent application, and assigned his interest in the application—as well as in any future "continuation applications"—to Novacept.1 The NovaSure System, as described in Truckai's patent application, uses an applicator head to destroy targeted cells in the uterine lining. To avoid unintended burning or ablation (tissue removal), the head is "moisture permeable," meaning that it conducts fluid out of the uterine cavity during treatment. The PTO issued a patent, and in 2001 the Food and Drug Administration (FDA) approved the device for commercial distribution. But neither Truckai nor Novacept currently benefits from the NovaSure System patent. In 2004, Novacept sold its assets, including its portfolio of patents and patent applications, to another company (netting Truckai individually about $8 million). And in another sale, in 2007, respondent Hologic, Inc. acquired all patent rights in the NovaSure System. Today, Hologic sells that device throughout the United States.

Not through with inventing, Truckai founded in 2008 petitioner Minerva Surgical, Inc. There, he developed a supposedly improved device to treat abnormal uterine bleeding. Called the Minerva Endometrial Ablation System

, the device (like the NovaSure System) uses an applicator head to remove cells in the uterine lining. But the new device, relying on a different way to avoid unwanted ablation, is "moisture impermeable": It does not remove any fluid during treatment. The PTO issued a patent for the device, and in 2015 the FDA approved it for commercial sale.

Meanwhile, in 2013, Hologic filed a continuation application requesting to add claims to its patent for the NovaSure System. Aware of Truckai's activities, Hologic drafted one of those claims to encompass applicator heads generally, without regard to whether they are moisture permeable. The PTO in 2015 issued the altered patent as requested.

A few months later, Hologic sued Minerva for patent infringement. Minerva rejoined that its device does not infringe. But more relevant here, it also asserted that Hologic's amended patent is invalid. The essential problem, according to Minerva, is that the new, broad claim about applicator heads does not match the invention's description, which addresses their water-permeability. See Defendant Minerva's Opening Brief in Support of Its Motion for Partial Summary Judgment in No. 15–cv–1031 (Del.), Doc. 300, pp. 8–9, 13–15; see also Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co. , 535 U.S. 722, 736, 122 S.Ct. 1831, 152 L.Ed.2d 944 (2002) ("What is claimed by the patent application must be the same" as what is described). In response, Hologic invoked the doctrine of assignor estoppel. Because Truckai assigned the original patent application, Hologic argued, he and Minerva (essentially, his alter-ego) could not impeach the patent's validity. The District Court agreed that assignor estoppel barred Minerva's invalidity defense, and also ruled that Minerva had infringed Hologic's patent. See 325 F.Supp.3d 507, 524–525, 532 (D.Del. 2018). At a trial on damages, a jury awarded Hologic about $5 million.

The Court of Appeals for the Federal Circuit mainly upheld the judgment, focusing on assignor estoppel. The court first "decline[d] Minerva's invitation to ‘abandon [that] doctrine.’ " 957 F.3d 1256, 1267 (2020). Citing both this Court's precedents and equitable principles, the court affirmed the doctrine's "continued vitality." Id., at 1268. An assignor, the court stated, "should not be permitted to sell something and later to assert that what was sold is worthless, all to the detriment of the assignee." Id. , at 1265. The assignor makes an "implicit representation" that the rights "he is assigning (presumably for value) are not worthless." Ibid. It would "work an injustice," the court reasoned, to "allow the assignor to make that representation at the time of assignment (to his advantage) and later to repudiate it (again to his advantage)." Ibid. (quoting Diamond Scientific Co. v. Ambico, Inc. , 848 F.2d 1220, 1224 (CA Fed. 1988) ). The court then applied assignor estoppel to bar Truckai and Minerva from raising an invalidity defense. Here, the court rejected Minerva's argument that because "Hologic broadened the claims" after "Truckai's assignment," it would "be unfair to block Truckai (or Minerva) from challenging the breadth of those claims." 957 F.3d at 1268. Relying on circuit precedent, the court deemed it "irrelevant that, at the time of the assignment, the inventor's patent application[ ] w[as] still pending" and that the assignee "may have later amended the claims" without the inventor's input. Ibid. (quoting Diamond Scientific , 848 F.2d at 1226 ).

We granted certiorari, 592 U.S. ––––, 141 S.Ct. 975, 208 L.Ed.2d 510 (2021), to consider the important issues raised in the Federal Circuit's judgment. Assignor estoppel, we now hold, is well grounded in centuries-old fairness principles, and the Federal Circuit was right to uphold it. But the court failed to recognize the doctrine's proper limits. The equitable basis of assignor estoppel defines its scope: The doctrine applies only when an inventor says one thing (explicitly or implicitly) in assigning a patent and the opposite in litigating against the patent's owner.


Courts have long applied the doctrine of assignor estoppel to deal with inconsistent representations about a patent's validity. The classic case (different in certain respects from the one here) begins with an inventor who both applies for and obtains a patent, then assigns it to a company for value. Later, the inventor/assignor joins a competitor business, where he develops a similar—and possibly infringing—product. When the assignee company sues for infringement, the assignor tries to argue—contrary to the (explicit or implicit) assurance given in assigning the patent—that the invention was never patentable, so the patent was never valid. That kind of about-face is what assignor estoppel operates to prevent—or, in legalese, estop. As one of the early American courts to use the doctrine held: The assignor is not "at liberty to urge [invalidity] in a suit upon his own patent against a party who derives title to that patent through him." Woodward v. Boston Lasting Mach. Co. , 60 F. 283, 284 (CA1 1894). Or as the Federal Circuit held in modern times: The assignor's explicit or "implicit representation" that the patent he is assigning is "not worthless ... deprive[s] him of the ability to challenge later the [patent's] validity." Diamond Scientific , 848 F.2d at 1224.

Assignor estoppel got its start in late 18th-century England and crossed the Atlantic about a hundred years later. In the first recorded case, Lord Kenyon found that a patent assignor "was by his own oath and deed estopped" in an infringement suit from "attempt[ing] to deny his having had any title to convey." Oldham v. Langmead (1789), as described in J. Davies, Collection of the Most Important Cases Respecting Patents of Invention and the Rights of Patentees 442 (1816); see Hayne v. Maltby , 3 T. R. 439, 441, 100 Eng. Rep. 665, 666 (K. B. 1789) (recognizing the Oldham holding). That rule took...

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