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PTO memo limits evidence in IPR proceedings
The U.S. Patent and Trademark Office (PTO) announced this past summer that it would begin limiting the use of “applicant admitted prior art” (AAPA) in inter partes reviews (IPRs). The change came on the heels of a ruling by the U.S. Court of Appeals for the Federal Circuit that, contrary to the PTO’s new position, allowed such evidence to show missing claim limitations.
The court ruling
On July 14, 2025, the Federal Circuit issued its opinion in a case that involved an IPR challenge to a patent for a device for treating atherosclerosis. The device adds electrodes and a pulse generator to a “typical over-the-wire angioplasty balloon catheter.” The challenger argued that the device would have been obvious to a person with ordinary skill in the field (a “skilled artisan”).
Specifically, the challenger contended that it’d be obvious to modify a certain piece of prior art with the typical catheter. Prior art is existing material that would have made a patented invention obvious and thus unpatentable. AAPA is prior art referenced in a patent application; in this case, the catheter was the AAPA. The patent holder maintained that the Patent Trial and Appeal Board (PTAB) improperly relied on the AAPA in finding its patent claims obvious.
The Federal Circuit acknowledged that the only types of prior art that can be considered in IPRs are patents and printed publications. It also reiterated its holding in an earlier case that AAPA can’t be the basis of an unpatentability ground in an IPR petition.
But the court noted that the obviousness analysis requires an assessment of the “background knowledge” a skilled artisan would possess. And background knowledge can supply “missing claim limitations,” meaning claim limitations in the challenged patent that weren’t previously disclosed by the prior art.
The court concluded the challenger used background knowledge only to supply missing claim limitations — not to support unpatentability grounds. Therefore, the court found the use of the AAPA as evidence of the background knowledge was permissible.
The PTO memo
Barely two weeks later, though, the PTO released a significant memo regarding its approach to AAPA in the IPR context. Most importantly, the memo explicitly states that AAPA can’t be used to supply a missing claim limitation.
The memo supersedes 2020 and 2022 PTO memos that both waived PTAB enforcement of Rule 104(b)(4), which requires an IPR petition to specify “where each element of the claim is found in the prior art patents or printed publications relied upon.” The rule is now back in effect for any petition filed on or after September 1, 2025.
The memo labels AAPA, expert testimony, common sense and other evidence that isn’t prior art in the form of patents or printed publications as “general knowledge.” According to the memo, such general knowledge can be used in an IPR only to support a motivation to combine prior art or to demonstrate the knowledge of a person having ordinary skill in the art.
Going forward
The PTO’s memo has critical implications for patent applicants, patent holders and IPR challengers. For all these parties, thorough checks of prior art are more important than ever.
© 2025
