Doctrine of Equivalents in Patent Prosecution: DOE Application, Festo Exceptions, Recent Case Law Developments

Recording of a 90-minute premium CLE webinar with Q&A

Conducted on Thursday, December 5, 2019

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Program Materials

This CLE webinar will guide patent counsel on the doctrine of equivalents (DOE). The panel will discuss recent Federal Circuit DOE decisions applying the “tangential relation” exception: Ajinomoto Co. v. ITC (Fed. Cir. 2019) and Eli Lilly & Co. v. Hospira, Inc. (Fed. Cir. Aug. 9, 2019), As the court held in Lilly, “whether an amendment was merely tangential to an equivalent must be decided in the context of the invention disclosed in the patent and the prosecution history."


The DOE is a judicial doctrine that permits a court to find infringement when an accused product or process falls outside of the literal language of the claims but is equivalent to and differs only insubstantially from the claimed invention. The concept of something infringing when the accused product "performs substantially the same function in substantially the same way to obtain the same result" can be found as far back as Sanitary Refrigerator Co. v. Winters, 280 U.S. 30, 42 (1929).

Prosecution history can operate as a limit on DOE. "The doctrine of prosecution history estoppel serves to limit the doctrine of equivalents when the applicant makes a narrowing amendment for purposes of patentability, or clearly and unmistakably surrenders subject matter by arguments made to the examiner." Salazar v. Procter & Gamble Co. (Fed. Cir. 2005). The rationale for this principle is that the patentee should not be allowed to gain through the DOE claim scope that it gave up during prosecution to obtain allowance of the claims.

According to the U.S. Supreme Court in Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushki Co. (2002) (Festo VIII), however, a patentee can rebut the presumption that prosecution history estoppel applies if it shows that it comes within one of three exceptions. These exceptions are: the equivalent was unforeseeable at the time of the application, the rationale underlying the amendment bears no more than a tangential relation to the equivalent in question, or some other reason suggesting that the patentee could not reasonably be expected to have described the insubstantial substitute in question.

Listen as our authoritative panel examines the lessons from Federal Circuit decisions for practitioners arguing for or against the application of the Festo exceptions, as well as more broadly for or against applying the DOE. The panel will discuss recent Federal Circuit DOE decisions Eli Lilly v. Hospira (Fed. Cir. 2019) and Ajinomoto v. ITC (Fed. Cir. 2019) applying the tangential relation exception. The panel will also look at earlier Federal Circuit decisions applying the Festo framework, as well as other judicial decisions applying the DOE outside the confines of the doctrine of prosecution history estoppel. The panel will discuss a more recent decision addressing the hypothetical claim analysis or ensnarement in Janssen Biotech Inc. v. Celltrion Healthcare Co. Ltd. (D. Mass. 2018), appeal pending (18-2350).



  1. DOE decisions
    1. Early cases: policy considerations
  2. Estoppel: Festo and its progeny
  3. Exceptions
    1. The equivalent was unforeseeable at the time of the application
    2. Tangential relation
    3. An unreasonable expectation to describe the insubstantial substitute
  4. Issues that could reduce the chance of the patentee proving infringement by the DOE
  5. Hypothetical claims and other alternatives
    1. Wilson Sporting Goods Co. v. David Geoffrey & Assocs., 904 F.2d 677 (Fed. Cir. 1990)
    2. Janssen Biotech Inc. v. Celltrion Healthcare Co. Ltd., 17-cv-11008 (D. Mass. July 30, 2018), appeal pending (18-2350)


The panel will review these and other important issues:

  • Early DOE decisions: the policy considerations
  • Modern file history estoppel from Festo and its progeny
  • Hypothetical claims and other alternatives to substantially the same function, way, and result, such as quality, purpose, and function


Irving, Thomas
Thomas L. Irving

Finnegan Henderson Farabow Garrett & Dunner

Mr. Irving has 35 years of experience in the field of IP law. His practice includes due diligence, patent prosecution,...  |  Read More

Jakes, J. Michael
J. Michael Jakes

Finnegan Henderson Farabow Garrett & Dunner

Mr. Jakes concentrates his practice on patent litigation and related counseling. He serves as lead counsel in federal...  |  Read More

McCurdy, Barbara
Barbara Clarke McCurdy

Finnegan Henderson Farabow Garrett & Dunner

Ms. McCurdy has more than 25 years of experience creating, enforcing, and defending patent rights, with a particular...  |  Read More

Murphy, Amanda
Amanda K. Murphy, Ph.D.

Finnegan Henderson Farabow Garrett & Dunner

Dr. Murphy focuses her practice on client counseling and patent prosecution for a range of clients. She prepares new...  |  Read More

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