Infringement under the Doctrine of Equivalents is Barred by Prosecution History Estoppel

The Federal Circuit recently affirmed dismissal of the patent owner’s lawsuit brought for patent infringement under the doctrine of equivalents in Amgen Inc. v. Coherus Biosciences Inc., 2018-1993 (Fed. Cir. July 29, 2019).  The case illustrates one of the potential difficulties a patent owner may encounter under the doctrine of equivalents.  Prosecution history estoppel is a defense to a charge of infringement under the doctrine of equivalents, and prevents a patent owner from recapturing subject matter surrendered  from the literal scope of a claim during prosecution.  It occurs in two ways.  First, and most common, is by the patent applicant making a narrowing amendment to the claim – commonly referred to as amendment based estoppel.  The second way is by surrendering  claim scope through arguments made during prosecution – referred to as argument based estoppel.  In order for argument based estoppel to apply, the prosecution history must “evince a clear and unmistakable surrender of subject matter.”

In the Amgen case, the Federal Circuit determined that argument based estoppel did apply.  The Court’s ruling was based on arguments made by the patent applicant to overcome the cited prior art in which the applicant stated the prior art did not teach or suggest the “particular combinations of [chemical materials]” recited in the pending claims.  Additionally, during prosecution, the applicant submitted a declaration that described the combination of chemical materials as “particular dual salt combination[s]”.  The Court agreed with the District Court of Delaware that “ competitor would reasonable believe” that the patent owner surrendered unclaimed combinations.  Ultimately the Federal Circuit concluded the disavowal was a “clear and unmistakable surrender.”