Supreme Court Grants Certiorari to Resolve Long-Running Debate on Assignor Estoppel

By: David G. Barker and Emily R. Parker

Last Friday, the U.S. Supreme Court granted certiorari in Minerva Surgical v. Hologic, thereby agreeing to resolve a long-running debate on patent law’s doctrine of assignor estoppel. Minerva Surgical has asked the Court to abolish the doctrine, which bars inventors who sell their patent rights from challenging the patent’s validity in district court.

The inventor in this case, Csaba Truckai, co-founded a company called NovaCept and developed two patents for endometrial ablation, a surgical process used to treat menstrual bleeding. NovaCept sold its patents to Cytyc Corp., which was acquired by Hologic. Then Truckai formed Minerva Surgical, which developed a competing ablation system. Hologic sued for infringement, asserting the two NovaCept patents. The district court ruled that Minerva could not challenge the validity of Hologic’s patents, because Truckai was barred by assignor estoppel from attacking his own patents. The jury found that Minerva infringed both patents and awarded Hologic $4.8 million in damages.

Meanwhile, Minerva succeeded in invalidating one of the NovaCept patents in an inter partes review (“IPR”) at the Patent Trial and Appeal Board (“PTAB”), because assignor estoppel does not apply there. Because the PTAB invalidated the patent, the district court denied Hologic’s request for a permanent injunction against Minerva as moot, but the damages award remained in place. The U.S. Court of Appeals for the Federal Circuit affirmed the decision, with Judge Kara Stoll writing that the court was “mindful of the seeming unfairness to Hologic in this situation”: 

Given the odd circumstance created in this case, I suggest that 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. We should seek 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 Federal Circuit declined to take up the matter, but now the Supreme Court has.

The Supreme Court will consider “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.” Minerva argues that an invalidity defense is warranted here because the new owner Hologic “broadened the scope of the patent beyond anything the inventor had claimed.” This is an important case to follow, because it may affect the considerations involved in assigning and determining the value and scope of patent rights.

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