U.S. Supreme Court Narrows Assignor Estoppel Doctrine In Continuation Patent Case

Now, nearly a century later, the Court ruled that it is time to narrow the scope of assignor estoppel. In its decision authored by Justice Elena Kagan, the Court concluded that assignor estoppel applies "when, but only when, the assignor's claim of invalidity contradicts explicit or implicit representations he made in assigning the patent." Minerva, slip op. at 1

The Facts

In Minerva, an inventor created a medical device, founded a company (Novacept, Inc.) to sell the device, filed a patent application for the device, and assigned the company his interest in the patent application, as well as any future continuation applications. Novacept later sold its patent and patent application portfolio to another company, which in turn sold the patent rights for the medical device to Hologic, Inc. The inventor later founded Minerva Surgical, Inc. and developed another medical device that allegedly improved the version he patented and sold just a few years earlier. As a result, Hologic sued Minerva Surgical for patent infringement of one of its continuation patents. As a defense to infringement, Minerva Surgical argued that the continuation patent for the medical device is invalid. In turn, Hologic invoked the doctrine of assignor estoppel. Both the district court and the Federal Circuit found that assignor estoppel barred Minerva Surgical's invalidity defense. See, Hologic, Inc. v. Minerva Surgical, Inc., 325 F. Supp. 3d 507 (D. Del. 2018); Hologic, Inc. v. Minerva Surgical, Inc., 957 F. 3d 1256, (Fed. Cir. 2020).