A person who assigns his or her patent to another may not later attack the validity of that patent in district court, under the doctrine of assignor estoppel. But an assignor may, under some circumstances, attack the patent in a proceeding before the Patent Office. Last month, in Hologic v. Minerva Surgical, Judge Kara Farnandez Stoll suggested that the en banc Federal Circuit should address the “odd and seemingly illogical regime” in which “an assignor can circumvent the doctrine of assignor estoppel by attacking the validity of a patent claim in the Patent Office, but cannot do the same in district court.” No. 2019-2054, 2020 WL 1932944, at *13-14 (Fed. Cir. April 22, 2020) (Stoll, J., additional views).
We report here on Hologic and on another recent Federal Circuit case that addressed the scope of assignor estoppel, Arista Networks v. Cisco Systems, 908 F.3d 792 (Fed. Cir. 2018), because the doctrine is significant for attorneys advising clients in transferring patent rights.
Assignor Estoppel
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