Assignor estoppel is an equitable defense that prevents an assignor of a patent from later challenging the patent's validity. In Arista Networks, Inc. v. Cisco Systems, Inc., No. 17-1525 (Fed. Cir. Nov. 9, 2018), the Federal Circuit held that assignor estoppel does not apply in IPR proceedings. Arista petitioned for IPR of a patent invented by a former Cisco employee that assigned his rights in the invention to Cisco and subsequently left Cisco to co-found Arista. The PTAB issued a final written decision rejecting Cisco's argument that Arista's petition should be denied based on assignor estoppel, pointing to earlier Board decisions explaining that 35 U.S.C. § 311(a) allows IPR petitions to be filed by any person who is not the patent owner.
On appeal, the Federal Circuit first considered whether this issue was reviewable under 35 U.S.C. § 314(d). The Federal Circuit determined that the issue of whether § 311(a) contemplates application of assignor estoppel was reviewable because it did not relate to the merits of Arista's petition or the PTAB's preliminary patentability determination. The Court found that the plain language of § 311(a) demonstrates that an assignor, who is no longer the owner of a patent, may file an IPR petition as to that patent. Thus, the Court concluded that § 311(a) unambiguously dictates that assignor estoppel has "no place" in IPR proceedings.
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