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Supreme Court Determines New Limitations to Assignor Estoppel Doctrine

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By Marsha Cotton and David G. Barker

The Supreme Court upheld assignor estoppel in Minerva Surgical, Inc. v. Hologic, Inc., et al. but held that the Federal Circuit “failed to recognize the doctrine’s proper limits.” In doing so, the Court imposed new limitations on when the equitable doctrine applies in a patent case.

The Court did away with the bright-line rule that any time an inventor assigns a patent, he or she cannot later argue that the patent is invalid. Previously, courts applied the rule without looking to the individual facts and circumstances in each case. But the Court held that a fact-specific review is required when determining whether to apply the doctrine because it is rooted in equitable principles.

In the late 1990s, Petitioner Minerva’s founder, Csaba Truckai, invented a device to treat abnormal uterine bleeding and filed a patent application on the device. He later assigned the application, along with any future continuation applications, to his employer, Novacept, Inc. Respondent Hologic, Inc. then acquired Novacept, along with its portfolio of patents and patent applications.

In 2008, Truckai founded Minerva and received FDA approval to sell an improved device to treat abnormal uterine bleeding. Around the same time, Hologic filed a continuation application to add claims to the original patent; the continuation issued in 2015. Hologic then sued Minerva for patent infringement, but Minerva argued that Hologic’s patent was invalid because the continuation’s claims did not match the invention’s original written description. In response, Hologic asserted assignor estoppel. The District Court agreed that assignor estoppel barred Minerva’s invalidity defense, and the Federal Circuit affirmed.

Before the Supreme Court, Minerva argued that Hologic’s new claim expanded on Truckai’s original invention, so it should be allowed to challenge the patent. Minerva further argued that federal legislation and two prior Supreme Court cases already “interred” assignor estoppel, so the rule should be abandoned. In contrast, Hologic argued that assignor estoppel is well-settled law, and it was appropriately applied in this case.

In a split 5-4 opinion by Justice Elena Kagan, the Supreme Court held that challenges by the inventor of a patent may be appropriate in some cases, including when the patent at issue is “materially broader” than what was assigned. The Court remanded to the Federal Circuit to determine whether the Hologic patent at issue was materially broader than what Truckai originally assigned. The Court explained that this threshold issue must be decided to “determine whether assignor estoppel applies.” The Court also held that assignor estoppel does not apply to patent assignments in common employment agreements in which an employee agrees to assign to the employer all future inventions developed on the job. The Court reasoned that the assignor estoppel doctrine cannot apply where a patent does not even exist. Notably, the Court declined to determine whether assignor estoppel applies at hearings before the Patent Trial and Appeal Board.