Archive:May 13, 2025

The Federal Circuit recently resolved a split among the district courts whether patent infringement defendants who bring inter partes review (IPR) challenges are estopped from raising new prior art challenges in a co-pending district court litigation. While some district courts had earlier found estoppel to have broad effect, and thus prevent challenges based on products on sale or public use, the Federal Circuit’s decision means that estoppel is limited only to challenges based on patents or printed publications, opening the door to use patents and publications to provide evidence of what subject matter was “on sale” or “in public use.”