Minerva Surgical v. Hologic: Supreme Court Retains but Narrows Assignor Estoppel

Picture this: someone offers to assign you the patent for a cutting-edge technology that could change the world. You leap at the prospect and buy the rights, only for the inventor to immediately declare the patent invalid. Now, you’re out millions of dollars and have potentially lost the ability to sell this novel technology. What can you do?

You may seek refuge in assignor estoppel. This legal doctrine forbids a patent’s assignor from claiming that the patent is invalid after assigning it to another party. The Supreme Court recognized assignor estoppel in the 1924 case Westinghouse Elec. & Mfg. Co. v. Formica Insulation Co., and the doctrine has been a key aspect of United States intellectual property law ever since. While assignor estoppel prevents assignors from unfairly reneging on agreements with assignees, it has questionable standing as a legal doctrine. For example, it’s unclear whether the United States Patent Act of 1952 allows assignor estoppel to continue. Section 282 of the Patent Act states that invalidity “shall be [a] defense[] in any action” involving infringement. The word “any,” of course, implies that invalidity is a legitimate defense in all cases. So, doesn’t the Patent Act give assignors the right to claim invalidity in infringement disputes?

This question was a central issue in the recent Supreme Court case Minerva Surgical v. Hologic. In Minerva, an inventor named Csaba Truckai created two surgical devices with moisture-permeable heads designed to treat heavy menstrual bleeding. Truckai assigned the patent applications to his company, Novacept, which was later taken over by Hologic. Eventually, Truckai left Hologic to found another company, Minerva Surgical, where he invented a new device with a moisture-impermeable head. Aware of Truckai’s competing device, Hologic filed a continuation application to broaden its claims on the original technology and obtain the rights to devices with moisture-impermeable heads as well. After receiving the continuation patent, Hologic sued Minerva Surgical for patent infringement. Minerva responded that the continuation patent was invalid because it covered features not present in the original patent, and Hologic, in turn, invoked the principle of assignor estoppel. At district court, the jury awarded Hologic $4.7 million dollars in damages for patent infringement, which led Minerva Surgical to appeal the decision, arguing that the assignor estoppel doctrine no longer applies in light of the 1952 Patent Act.

Above: Justice Elena Kagan, author of the majority opinion in Minerva Surgical v. Hologic

In a 5–4 decision, the Supreme Court upheld the assignor estoppel doctrine but narrowed its scope, and remanded the case for further consideration. Elena Kagan, delivering the court’s majority opinion, wrote that “assignor estoppel applies only when the assignor’s claim of invalidity contradicts explicit or implicit representations he made in assigning the patent.” So, in Minerva, the court permitted an invalidity claim because Truckai did not represent the patent as applying to both moisture-permeable and impermeable heads when he assigned it; Hologic’s continuation patent substantially broadened the scope of Truckai’s original invention. Kagan also addressed the issue of the 1952 Patent Act in her opinion, writing that Congress often legislated in the mid-twentieth century “‘against a background of common-law adjudicatory principles,’ including assignor estoppel.” Thus, from the majority’s reading, assignor estoppel is implicit in the Patent Act.

So, you might be wondering, how will the Supreme Court’s decision affect me? Essentially, it offers certain assignors more flexibility in their defense for patent infringement cases. Assignors can now claim that patents are invalid if the assignee has expanded the scope of the patent beyond what was initially agreed upon. Meanwhile, assignees can breathe a sigh of relief that assignor estoppel remains in place, still preventing inventors from invalidating patents immediately after handing over their rights. And for assignors and assignees alike, the recent Minerva decision makes it all the more important to pay close attention to the representations being made at the time of assigning patent rights.