Proving anticipation or obviousness often entails aligning disclosure in the prior art with the elements of the challenged claim. However, when the claim includes a negative limitation, the task may be more complicated. References often positively describe devices, systems, methods, etc. and devote little, if any, attention to describing what those things lack. A patent challenger thus may be unable to muster explicit disclosure that a certain feature or step is omitted from a reference. Two recent Federal Circuit decisions provide useful guidance as to how a patent challenger may use a reference’s silence to show satisfaction of a negative limitation.
In In re Strongbridge Dublin Ltd., Appeal Nos. 2023-2302, -2303 (Fed. Cir. Mar. 10, 2025) (“Strongbridge”), the Federal Circuit held that a reference’s silence, standing alone, is not substantial evidence of the absence of a feature. In that appeal, the Federal Circuit reviewed the Board’s affirmance of an Examiner’s rejections of two similar claims during ex parte prosecution. The claims each recited a method of administering dichlorphenamide in a specific dosage and frequency. Each claim also included a negative limitation. Specifically, the claims recited “while also avoiding concomitant administration to said human patient of . . . famotidine” and “while also avoiding concomitant administration of methotrexate to said patient,” respectively. The Examiner rejected the claims based on a reference (Sansone) that described a clinical trial in which patients were administered dichlorphenamide in the dosage and frequency specified by the claims. The Board upheld the Examiner’s rejections, finding that Sansone does not mention famotidine or methotrexate, neither is a required drug in Sansone’s clinical trial, and the class of patients described in Sansone, i.e., those taking dichlorphenamide, was “unrelated” to the classes of patients who take famotidine or methotrexate.
The Federal Circuit reversed. It held that the Board’s findings are relevant “but not substantial evidence in and of themselves.” The Federal Circuit continued, “There must something more to suggest that the silence [of Sansone in disclosing famotidine or methotrexate] is significant, or other reasons that establish by a preponderance of the evidence that it is likely that one or more patients in the” clinical trial was not taking famotidine or methotrexate. The Board’s affirmance of the rejections was therefore vacated. For the Board’s consideration on remand, the Federal Circuit offered suggestions as to what may suffice for the “something more” than Sansone’s silence. For example, the Federal Circuit noted that the “the structure of the study, the results of the study, or statistical analysis as to the likelihood that at least one patient was not taking famotidine or methotrexate” may support the rejections. Additionally, the Federal Circuit noted that Sansone discloses that only one of the patients experienced gastroesophageal reflux disease, for which famotidine is indicated. The Federal Circuit volunteered that this “perhaps suggest[s] that other patients were not taking famotidine.” Similarly, the Federal Circuit noted that Sansone reported certain adverse events (e.g., neoplasms, rash, pain, and musculoskeletal and connective tissue disorders) and that this might be relevant to whether patients in the Sansone trial were taking methotrexate. In short, the Federal Circuit indicated that Sansone’s silence coupled with circumstantial evidence may suffice to sustain the rejections. However, Sansone’s silence standing alone is not.
By contrast, in United Services Auto. Assoc. v. PNC Bank N.A., Appeal No. 2023-2244 (Fed. Cir. Mar. 5, 2025) (“USAA”), the Federal Circuit found that a reference’s silence—coupled with evidence as to what that silence implied—was substantial evidence to uphold a finding of unpatentability. USSA came to the Federal Circuit on appeal from an Inter Partes Review proceeding initiated by PNC Bank (“PNC”). PNC challenged claims of a USAA patent directed at remotely depositing checks. One of the challenged claims recited, among other things, receiving an image of a back side of a check captured by a camera, processing the image of the back side of the check to determine whether a mark is present on the image, and “determining whether a mark is present at an endorsement location in the image of the back side of the check without further performing a signature identification procedure.” PNC argued that prior art reference Randle disclosed that limitation. USAA countered that PNC was relying on Randle’s silence as evidence that it allegedly taught the negative limitation.
The Federal Circuit sided with PNC. Specifically, the Federal Circuit found that the Board had relied on Randle’s disclosure, the context of that disclosure, as well as the testimony of PNC’s expert Dr. Brian Noble. The Board found that Randle explicitly distinguishes (i) determining the presence of a check writer’s signature on the front of the check and verifying that signature from (ii) merely checking from the presence of the payee’s endorsement on the back of the check. Further, Dr. Noble testified that a person of ordinary skill in the art would understand that Randle’s process did not involve performing signature identification on the endorsement location. Thus, the Federal Circuit found that “the Board’s conclusion is not founded solely on Randle’s silence.”
Strongerbridge and USAA illustrate that a reference’s silence alone likely will not be viewed as sufficient disclosure of a negative limitation. However, these cases also make clear that a reference need not explicitly disclose a feature’s absence. Rather, a patent challenger may be able to meet their burden by coupling a reference’s silence with other, even circumstantial, evidence.