Hologic, Inc., et al. v. Minerva Surgical, Inc.

American courts have long relied on the doctrine of assignor estoppel “to prevent unfairness and injustice.” Diamond Sci. Co. v. Ambico, Inc., 848 F.2d 1220, 1224 (Fed. Cir. 1988) (citation omitted). In its most basic form, the doctrine “prohibits an assignor of a patent, or one in privity with an assignor, from attacking the validity of that patent when he is sued for infringement by the assignee.” MAG Aerospace Indus., Inc. v. B/E Aerospace, Inc., 816 F.3d 1374, 1379-80 (Fed. Cir. 2016). At the rule’s heart lies a straightforward intuition: “an assignor should not be permitted to sell something and later to assert that what was sold is worthless, all to the detriment of the assignee.” Diamond Sci., 848 F.2d at 1224. Under the Patent Act and the America Invents Act, a party may challenge the validity of an issued patent not only in infringement litigation in district court, but also through administrative proceedings before the Patent Office. The Federal Circuit has held that the Patent Office’s administrative finding of invalidity can give rise to collateral estoppel in infringement litigation in district court. The question presented is whether an assignor of a patent may circumvent the doctrine of assignor estoppel by challenging the validity of the assigned patent in administrative proceedings before the Patent Office, and then using the Patent Office’s finding of invalidity to collaterally estop the assignee from relying on the patent in infringement litigation in district court. (I)