On March 18, 2016, Judge Lefkow of the U.S. District Court for the Northern District of Illinois held that the estoppel provision of 35 U.S.C. § 315(e)(2) does not extend to prior art that was not reasonably available during an inter partes review (“IPR”), even if that prior art is cumulative of prior art that was used during the IPR. This is a key decision addressing an issue of first impression. If affirmed by the Federal Circuit, or adopted as persuasive by other district courts, it could have a profound effect on IPR practice and patent litigation as a whole because, under certain circumstances, it gives petitioners an opportunity to retry in district court nearly the same invalidity arguments that they lost on in an earlier IPR.
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