After an Inter Partes Review (IPR) at the United Stated Patent and Trademark Office (USPTO) is completed, validity and/or infringement of the patent may subsequently be determined by a U.S. district court. This situation raises the significant issue of what prior art may be asserted in the district court suit. A district court in Illinois recently determined the mere fact that prior art is cumulative of IPR cited prior art does not foreclose the cumulative art from being used in a district court suit.