On 21 April 2021 the Supreme Court heard oral argument in
Minerva Surgical Inc v Hologic Inc (20-440), a case that could limit or eliminate the doctrine of assignor estoppel. Assignor estoppel is a common law doctrine that prevents, in district court patent litigation, the assignor of a patent from challenging the validity of the assigned patent as a defence to infringement allegations. The Federal Circuit has previously held that while assignor estoppel may apply in district court litigation, it cannot bar an assignor from challenging patent validity in an
inter partes review at the United States Patent and Trademark Office (USPTO).