Minerva Surgical, Inc., filed a petition for certiorari with the U.S. Supreme Court asking the court to clarify questions around the doctrine of assignor estoppel. Their petition asks “Whether a defendant in a patent infringement action who assigned the patent, or is in privity with an assignor of the patent, may have a defense of invalidity heard on the merits.” The Supreme Court granted the petition.

Bottom line is that the doctrine of assignor estoppel is this: an inventor can’t sell patent rights to someone and then later insist that those rights are invalid.

Hologic, Inc. and Cytyc Surgical Products are respondents in the case and filed a cross-petition for certiorari. Their petition asks the court to answer “whether an assignor of a patent may circumvent the doctrine of assignor estoppel by challenging the validity of the assigned patent in administrative proceedings before the Patent Office, and then using the Patent Office’s finding of invalidity to collaterally estop the assignee from relying on the patent in an infringement litigation in district court.”

Csaba Truckai, co-founder of NovaCept, helped develop patents on endometrial ablation. The company and its patents were sold to Cytyc Corp. in 2004. Cytyc was acquired by Hologic. Truckai subsequently founded Minerva Surgical Inc., which developed a competing ablation system. Hologic sued for infringement on two of the NovaCept patents. U.S. District Judge Joseph Bataillon ruled in favor of Hologic, saying Minerva was estopped from challenging the validity of the patents in court.

Minerva did, however, succeed in invalidating one of the patents in an administrative proceeding. They went before the U.S. Patent and Trademark Office (USPTO), which doesn’t recognize assignor estoppel. The second patent has expired.

The U.S. Court of Appeals for the Federal Circuit (CAFC) reluctantly affirmed Judge Bataillon’s judgment, noting the seeming unfairness to Hologic. In that decision, Judge Kara Stoll wrote that the case pointed out an “odd situation where an assignor can circumvent the doctrine of assignor estoppel by attacking the validity of a patent claim in the Patent Office, but it cannot do the same in district court.” The judge noted that precedent in Arista v. Cicso (2018) held that the doctrine of assignor estoppel does not apply in the context of an IPR, but that the precedent in Mentor Graphics v. EVE-USA (2017) simultaneously precludes assignors from challenging the validity of their assigned patents in district court.

Judge Stoll wrote, “it is time for this court to consider en banc the doctrine of assignor estoppel as it applies both in district court and in the Patent Office,” to clarify this “odd and seemingly illogical regime in which an assignor cannot present any invalidity defenses in district court but can present a limited set of invalidity grounds in an IPR proceeding.” The en banc hearing was denied, and the parties petitioned the Supreme Court.

According to Minerva’s petition, “Assignor estoppel undermines, rather than serves, patent law values. Nonetheless, the Federal Circuit not only has continued to apply this textually groundless doctrine, it has expanded it at every opportunity.” Minerva wants the doctrine of assignor estoppel to be eliminated altogether. And despite the fact that assignor estoppel was created by the judiciary, since the Federal Circuit Court held in Arista that assignor estoppel does not apply in IPRs, the court is “at odds with itself.” The court previously rejected a similar doctrine, “licensee estoppel,” in 1969.

Minerva’s petition sets forth concerns about the way Hologic’s patent has been used. They ask the Court to either reject the assignor estoppel doctrine or define its “very limited contours.” Minerva says, “the Federal Circuit expanded assignor estoppel to bar petitioner Minerva from raising invalidity defenses that arose only because the ultimate assignee of the patent rights, respondent Hologic, had broadened the scope of the patent beyond anything the inventor had claimed.” Minerva does not assert that what the inventor assigned was worthless, but rather that the old assigned patent had been re-drafted and broadened far beyond its original scope. This broader, new patent, not the one originally assigned, has been used by Hologic when they “wielded that claim against Minerva.”

Hologic filed a cross-petition, which was not granted. In that petition, they argued that assignor estoppel is “a simple, intuitive rule” that “precludes inventors who have assigned (i.e., sold) the rights to an invention from later challenging the validity of the rights they sold.” The petition goes on to say that if the court grants Minerva’s request to eliminate the doctrine, it would be a “revolutionary step” and would remove a “baseline protection that this Court first endorsed almost a century ago and against which Congress has legislated.” Hologic’s suggestion is that to remove the assignor estoppel doctrine would “encourage duplicative litigation, forum shopping, and other forms of gamesmanship.”

Amicus briefs have been filed backing Minerva’s position. These briefs have been filed by Intellectual Property Professors (IPP) and Engine Advocacy, so far. The IPP brief says “he doctrine has expanded far beyond the metes and bounds of this Court’s increasingly narrow precedent, including to cases lacking any bad faith during negotiations and to cases where not only the inventor herself but also her privies are precluded from challenging an invalid patent.” Engine Advocacy argues that the doctrine protects “low-quality patents (e.g, patents that are vague, overbroad, claim what is known in prior art, or otherwise cover inventions that ought not be considered patentable) from scrutiny.”

The case is scheduled for argument before the Supreme Court of the United States during the October 2020-2021 term.