Applying The Doctrine of Argument-Based Estoppel, Federal Circuit Affirms District Court’s Dismissal Of Infringement Claims
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  • Applying The Doctrine Of Argument-Based Estoppel, Federal Circuit Affirms District Court’s Dismissal Of Infringement Claims

    On July 29, 2019, the Court of Appeals for the Federal Circuit (CAFC) issued an opinion affirming a decision of the District Court for the District of Delaware dismissing a patent-infringement complaint for failure to state a claim.  Amgen Inc. v. Computer Biosciences. Inc., __ F.3d __ (Fed. Cir. July 29, 2019).  The CAFC affirmed the District Court’s application of the doctrine of argument-based estoppel and held that the patent owner could not succeed on its infringement claim. 

    The patent owner applied for, and was granted, a patent relating to a process of purifying a protein for use in a biologic drug.  The patent claimed specific salt combinations that are useful in the process.  The U.S. Patent and Trademark Office (“USPTO”) initially rejected the claims in the patent application as obvious on the basis that the prior art disclosed that salts are useful for purifying proteins and that a person of ordinary skill would be able to achieve the claimed invention through routine optimization to identify the claimed salts.  The patent owner successfully argued at the USPTO that (1) use of the specific claimed salt combinations greatly reduces the cost of the process, (2) choosing a working salt combination was a lengthy development path, and (3) merely adding a second salt to the prior art would not result in the invention.  The USPTO granted the patent. 

    In August 2016, the patent owner discovered that a competitor intended to use a salt combination in a protein-purification process, albeit not one of the specific combinations that were recited in the patent owner’s claims.  On May 10, 2017, the patent owner sued its competitor for infringement.  It alleged infringement only under the doctrine of equivalents, because the salt combination the competitor used did not match the claimed combination.  The competitor then moved to dismiss the complaint under Federal Rule of Civil Procedure 12(b)(6).  The District Court held that the prosecution history shows a clear and unmistakable surrender of claim scope beyond the claimed salt combinations, and that accordingly, prosecution history estoppel barred the patent owner from asserting the doctrine of equivalents against other salt combinations.

    In its opinion, the CAFC noted that prosecution history estoppel—which is an issue for the court, not a jury—can occur by surrendering claim scope through argument to the USPTO (“argument-based estoppel”).  Argument-based estoppel requires that the prosecution history “evince a clear and unmistakable surrender of subject matter.”  The relevant inquiry is “whether a competitor would reasonably believe that the applicant had surrendered the relevant subject matter.”    

    The patent owner’s primary argument at the CAFC was that during prosecution, it asserted multiple grounds for distinguishing the prior art, not just the argument to which its competitor was pointing.  The CAFC rejected this argument, noting that “our precedent instructs that estoppel can attach to each argument.”  Id. at 11.  Further, the Court explained that the patent owner “did not rely on the combination of its asserted grounds to distinguish [the prior art], so prosecution history estoppel applies to the “particular combinations” ground regardless of the other two arguments ….”  Id.  

    The District Court’s early engagement with the prosecution-history estoppel argument via the accused infringer’s motion to dismiss should be encouraging to patent defendants.  However, it remains to be seen whether district courts will be increasingly willing to address other infringement issues, such as patent claim construction, via motions to dismiss.