Estoppel is Not Invoked Simply Because Prior Art is Cumulative

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.

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