The US Court of Appeals for the Federal Circuit affirmed a Patent Trial & Appeal Board unpatentability determination during an inter partes review (IPR) proceeding, concluding that the Board’s decision to not apply interference estoppel fell within the general rule of unreviewability. IGT v. Zynga Inc., Case No. 23-2262 (Fed. Cir. July 22, 2025) (Prost, Reyna, Taranto, JJ.)

IGT owns an expired patent that addresses the need for gaming machines, such as slot machines and video poker machines, to securely communicate over a public network. The patent was issued in January 2007 from an application filed in April 2002 and published in August 2002. Zynga filed a patent application on August 21, 2003, that included claims copied from IGT’s published application.

In March 2010, the US Patent & Trademark Office (PTO) Board of Patent Appeals & Interferences (predecessor of the Patent Trial & Appeal Board, which Congress created in 2011) declared an interference proceeding between Zynga’s application and IGT’s patent. During the interference proceeding, Zynga argued IGT’s patent was obvious over three pieces of prior art. IGT argued that Zynga lacked standing because the claims in Zynga’s application were unpatentable for a lack of written description. The Board granted IGT’s motion for judgment on the “threshold issue” that Zynga’s application lacked adequate written description support, terminated the interference with a judgment against Zynga, and dismissed the motion that the claims were unpatentable as moot.

In April 2021, IGT sued Zynga alleging infringement of six patents, including the patent that was subject to the interference proceeding. Zynga filed an IPR petition for that patent, asserting obviousness based on new prior art. In its preliminary response, IGT argued that the Board should deny institution based on interference estoppel under 37 C.F.R. § 41.127(a)(1) because Zynga could have raised the newly asserted art in the interference proceeding. The Board rejected IGT’s interference estoppel arguments because:

• The interference was terminated based on the “threshold issue” of lack of written description and therefore the Board did not analyze or decide any issues of unpatentability.
• It would be unfair to estop Zynga, and to the extent that estoppel applied, the Board waived its application under 37 C.F.R. § 42.5(b).

IGT requested rehearing and precedential opinion panel review, arguing that interference estoppel barred institution. The PTO Director affirmed the Board’s decision, stating that interference estoppel under § 41.127 did not apply because IPR proceedings are governed by 37 C.F.R. pt. 42, which does not incorporate Part 41 or its estoppel provisions. The PTO Director also noted that the Board’s termination was based on a threshold issue. The Board proceeded with the review and ultimately concluded that all the challenged claims were unpatentable as obvious. IGT appealed.

IGT argued that the Board and PTO Director erred in ruling that interference estoppel did not bar the petition and challenged the Board’s holding that the claims would have been obvious over the newly asserted prior art.

The Federal Circuit concluded that the interference estoppel determination fell within the general rule of unreviewability and that there was no reversible error to justify an exception. The Court explained that Congress gave the PTO Director power to decide IPR institution and that “[t]he determination by the Director whether to institute an inter partes review under [§ 314] shall be final and nonappealable.” The Court found that IGT’s arguments from the preliminary response, rehearing request, and response filed after institution all argued that interference estoppel should have barred the proceeding and consequently had institution as its “direct, immediate, express subject,” causing the institution decision to fall within the general unreviewability principle.

IGT also argued that because its interference estoppel argument relied on a PTO regulation and not a statutory provision, it was unrelated to institution. IGT argued that the Board’s inclusion of the estoppel argument in the final written decision permitted IGT to challenge institution. The Federal Circuit disagreed, finding that nothing in § 314(d) narrowed the unreviewability protection to statutory provisions. The Court noted that IGT did not suggest a logical reason as to why review of a statutory violation would be barred while review of an agency’s regulations would not be.

The Federal Circuit next considered the Supreme Court’s suggestion from Cuozzo Speed Technologies, LLC v. Lee that there might be exceptions to the general rule of unreviewability where an agency engaged in blatant violation of legal constraints or other shenanigans. The Court concluded that the PTO provided three separate reasons for not applying interference estoppel and found that the PTO did not engage in any shenanigans in making its determination.

Lastly, the Federal Circuit considered IGT’s challenge to the Board’s holding of obviousness over the two newly presented pieces of prior art and rejected IGT’s theories. Accordingly, the Court affirmed the Board’s unpatentability determination.