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

The DOE is a judicial doctrine that permits a court to find infringement when an accused product or process falls outside 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 limits 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. The panel will discuss the example of argument-based prosecution history estoppel found in Amgen Inc. v. Coherus Biosciences Inc. (Fed. Cir. 2019).

According to the U.S. Supreme Court in Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co. (2002) (Festo VIII), 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 another reason suggesting that the patentee could not be expected to describe the insubstantial substitute.

Listen as our authoritative panel examines the lessons from recent Federal Circuit decisions for practitioners arguing for or against the Festo exceptions and, more broadly, for or against applying the DOE. The panel will also discuss hypothetical-claim analysis and ensnarement, disclosure-dedication, and all-limitations rule.

I. Early DOE decisions; policy considerations

II. Estoppel

A.    Argument-based

B.    Amendment-based

III. Festo

A.    Exceptions

1.     The equivalent was unforeseeable at the time of the application

2.     Tangential relation

3.     An unreasonable expectation to describe the insubstantial substitute

IV. Hypothetical claims/ensnarement

V. Disclosure-dedication

VII. All-limitations rule

The panel will review these and other important issues:

• The reappearance of the Festo exceptions
• The return of ensnarement
• Best practices for drafting and prosecuting claims to minimize estoppel-preventing DOE arguments