In Minerva Surgical, Inc. v. Hologic, Inc., the Supreme Court held that that the doctrine of assignor estoppel “is well grounded in centuries-old fairness … [but] … “applies only when an inventor says one thing … in assigning a patent and the opposite in litigating against the patent’s owner.” Here, the inventor filed a patent application and assigned it to his then-company Novacept, Inc. The inventor later left Novacept and founded Minerva while Hologic eventually acquired the resulting patent portfolio. Hologic broadened the scope of patent claims well after the inventor’s assignment.
The district court and the Federal Circuit agreed with Hologic’s argument that the inventor was estopped from impeaching the patent’s validity. However, the Supreme Court held “Assignor estoppel comes with limits” providing three examples, including (1) assignments made before an inventor can make a warranty of validity, (2) arrangements requiring assignment of any future inventions developed during employment, and (3) post-assignment changes in patent claims (which was the situation in this case).