Minerva Ablation Lawsuit: Patent Fight, Supreme Court, and Remand

The Minerva ablation lawsuit was a patent infringement fight between medical device maker Hologic and startup Minerva Surgical over endometrial ablation devices used to treat heavy uterine bleeding. Hologic won a jury verdict of roughly $4.8 million in 2018, and after a 2021 Supreme Court ruling that reshaped the doctrine of assignor estoppel, the Federal Circuit reinstated the judgment on remand, bringing Minerva’s total liability to more than $7 million. Minerva kept selling its device because the patent at the center of the case had already expired.

How the Dispute Started

Inventor Csaba Truckai developed the NovaSure System in the late 1990s, a device that uses radiofrequency energy to destroy the uterine lining. He co-founded NovaCept in 1993 and assigned his patent rights to the company, including the applications that became U.S. Patent Nos. 6,872,183 and 9,095,348.¹ Cytyc Corporation bought NovaCept in 2004 for $325 million, and Hologic acquired Cytyc in 2007, taking control of the NovaSure patent portfolio.²

In 2008, Truckai founded Minerva Surgical and built a competing device, the Endometrial Ablation System (EAS). The NovaSure device uses a moisture-permeable applicator head; Minerva’s uses a moisture-impermeable one. That design difference sat at the center of the later legal fight.³ The FDA cleared Minerva’s EAS in July 2015 for the same clinical use as NovaSure.⁴

The Infringement Verdict

Shortly after Minerva’s device reached the market, Hologic sued in the U.S. District Court for the District of Delaware, claiming the EAS infringed the ‘183 and ‘348 patents.¹ The argument was direct. Truckai had invented the technology, assigned the patents, and then built a competing device using the same technology.

Minerva’s defense was that Hologic’s patents were invalid, pointing to prior art, lack of enablement, and inadequate written description. Hologic invoked assignor estoppel, the doctrine that stops an inventor who has sold a patent from later attacking its validity. The district court agreed and blocked Minerva’s invalidity arguments entirely.⁵

The 2018 jury found Minerva liable for infringement and awarded Hologic about $4.8 million: roughly $4.2 million in lost profits and $587,000 in royalties.⁶ The Federal Circuit affirmed, and Minerva took the case to the Supreme Court.

What the Supreme Court Decided

The Supreme Court heard argument on April 21, 2021, and issued its decision on June 29, 2021. By a 5–4 vote, in an opinion by Justice Elena Kagan, the Court declined to eliminate assignor estoppel, calling it “well grounded in centuries-old fairness principles.” An inventor who sells a patent implicitly vouches for its validity, and the Court treated a later invalidity attack as an unfair reversal of that warranty.⁵

The majority also narrowed the doctrine. Assignor estoppel applies “only when the assignor’s claim of invalidity contradicts explicit or implicit representations the assignor made in assigning the patent.”⁷ The Court identified three situations where no such contradiction exists:

An employee assigns rights to future inventions before any specific patent claims are formulated, so nothing particular has been warranted.
A post-assignment change in patent law makes the original warranty of validity irrelevant.
The patent owner later expands the patent’s claims at the Patent and Trademark Office, so the inventor never warranted the validity of those broader claims.

The third exception was the one that mattered for Minerva. After Truckai’s assignment, Hologic had filed a continuation application adding new claims to the ‘348 patent broad enough to cover applicator heads regardless of whether they were moisture-permeable. The Federal Circuit had called it “irrelevant” whether Hologic had broadened the claims after assignment. The Supreme Court said that was wrong, vacated the judgment, and sent the case back to determine whether the new claims were “materially broader” than what Truckai had originally assigned.⁵

Justice Alito filed a solo dissent. Justice Barrett wrote a separate dissent joined by Justices Thomas and Gorsuch, arguing that the Patent Act of 1952 had abolished assignor estoppel entirely and that keeping a judge-made version alive lets bad patents survive.⁸

What Happened on Remand

On August 11, 2022, a Federal Circuit panel of Judges Stoll, Clevenger, and Wallach ruled that claim 1 of the ‘348 patent was not materially broader than what Truckai originally assigned. Reviewing the full prosecution history, including canceled claims, the court found that the subject matter of the broader claim had been part of the original application from the start. Because Truckai had signed an oath attesting to the patentability of the application as a whole, the broader claim “traveled with the application” and fell within his implied warranty of validity.⁹

Minerva remained estopped from challenging validity, and the Federal Circuit reinstated the original infringement judgment.¹⁰ Hologic said Minerva owed more than $7 million total, made up of the $4.8 million jury award, supplemental damages for continued sales through November 2018, and pre-judgment interest.¹¹

Why Minerva Kept Selling Its Device

Hologic won the damages fight but never got Minerva’s product pulled from the market. The ‘348 patent expired on November 19, 2018. The ‘183 patent claims were separately held invalid by the Federal Circuit in an April 2019 decision. With one patent expired and the other invalidated, the district court denied Hologic’s motion for a permanent injunction in May 2019.¹² The court also declined to award enhanced damages or attorney fees, finding the jury’s award adequate.⁶

After the Supreme Court ruling, Minerva said it was “free to continue selling its novel Minerva ES Endometrial Ablation Device as the Hologic patent at issue expired in November 2018.”¹³

The Countersuit Over Minerva’s Own Patent

The patent fight ran both ways. In 2018, Minerva sued Hologic, claiming that the NovaSure ADVANCED device infringed Minerva’s U.S. Patent No. 9,186,208. Hologic argued the ‘208 patent was invalid because the underlying invention had been publicly displayed more than a year before the patent application was filed.

The district court granted summary judgment to Hologic. It found that Minerva had shown its “Aurora” prototype at the American Association of Gynecologic Laparoscopists conference in November 2009 without confidentiality restrictions, and that the device was already “ready for patenting” then. Because the ‘208 patent’s priority date was November 7, 2011, more than a year after that public display, the patent was invalid under the public use bar.¹⁴ The Federal Circuit affirmed on February 15, 2023.¹⁵

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3
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