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In the recent precedential opinion, Colibri v. Medtronic,[1] the U.S. Court of Appeals for the Federal Circuit (CAFC) held that cancellation of a claim during patent prosecution can give rise to an estoppel effect on an issued patent claim which is separate from, but substantively related to, the cancelled claim, thereby affecting the scope of the issued claim when later asserted.

Prosecution History Estoppel and the Doctrine of Equivalents

The meaning of language in a patent claim may be subject to limitation by prosecution history estoppel (PHE), e.g., statements made on the record by the patent applicant to the Patent Office, typically to secure an allowance. Such statements may include explanations or arguments, or claim amendments made to overcome a rejection. The main concept underlying PHE is that once a patentee has clearly and unmistakably ceded subject matter during prosecution of the patent, it cannot recapture that subject matter to subsequently broaden the enforcement scope of the patent. Hence, courts take PHE into account when construing the meaning of claims asserted against an accused infringer.

In an infringement litigation, the patent claims are compared with an accused infringer’s product or process on an element-by-element basis, meaning that some claim elements may be literally infringed, while others not. “Equivalents” of non-literally infringing elements can be further established by the patentee under the Doctrine of Equivalents (DOE).

Equivalents of non-literally infringing elements are relevant to infringement when the accused product or process has “insubstantial differences,” which may be considered by whether the accused product performs substantially the same function as the claim element in substantially the same way, to accomplish substantially the same result.[2] However, a patentee’s equivalents arguments can be limited by PHE.[3] A situation where PHE may limit the DOE is where a patentee amended a claim element during prosecution, for example, to distinguish it from prior art, thereby creating a presumption they had ceded certain equivalents of the claim element.[4] The issue faced by the Colibri court was whether an amendment to a claim separate from the asserted claim can constitute PHE.

The Colibri v. Medtronic Decision

In Colibri, the technology at issue related to methods for placing artificial heart valves, which expand within a blood vessel after deployment from a sheath inserted into the vessel.[5] Particularly, the methods provided for restraining a valve from being fully deployed from the sheath during an initial placement such that the position of the valve could be adjusted, if necessary, before full, irreversible deployment.

At trial before the district court, Colibri won a $106 million verdict against Medtronic for inducing surgeons to infringe the asserted patent. This verdict rested upon a DOE theory.  Colibri asserted an independent claim reciting a method involving “pushing” the valve from the sheath,[6] whereas Medtronic’s method involved “retracting” the sheath while applying a retaining (i.e., pushing) force on the valve. The jury found Medtronic practiced an equivalent of Colibri’s asserted claim under the DOE, thereby finding infringement.

On appeal, the CAFC reversed the verdict. The CAFC determined that Colibri’s cancellation of a separate independent claim (referred to as “claim 39” in the opinion and herein) reciting “retracting” the sheath constituted PHE in interpreting the asserted claims.[7] In reaching this decision, the CAFC first disagreed with the district court’s conclusion that PHE did not apply. The district court had found that the asserted equivalent, i.e., both “pushing” and “retracting,” were distinct from the “retracting” set forth in claim 39, thereby obviating PHE applicability. The CAFC instead found that a countervailing force is necessary to push or restrain the valve relative to the sheath during retraction of the sheath from the blood vessel, else the valve would remain in the sheath during retraction.

The CAFC then formally determined that PHE can apply when a claim separate from, but substantively related to, the asserted claim is cancelled or otherwise amended. The CAFC rejected Colibri’s “formalistic” contention that the asserted claims had to be amended for PHE to apply, and proceeded to reverse the infringement verdict in favor of Medtronic. This precedential opinion establishes that PHE can apply not only when an asserted claim is amended or cancelled, but when any substantively related claim in the patent application having identical or similar claim element(s) is amended or cancelled.

Practical Implications for Patent Litigation and Prosecution

Colibri generally favors defendants in an infringement dispute. The PHE defense to a DOE assertion may now be more robust and wide-reaching. Defendants should carefully analyze all claims pending during prosecution, and particularly any amendments made after an Office Action has been issued. While not expressly discussed in the opinion, defendants should also seek to apply Colibri beyond the claims in the asserted patent(s) to capture cancellations and amendments made in any substantively related patent applications, including divisional and continuation applications.

On the patentee side, strategies are complicated by the separate Disclosure-Dedication Doctrine (DDD), which the Colibri court did not discuss. The DDD bars applicability of the DOE to unclaimed “alternative” claim elements described in the specification.[8] Should a patentee argue that elements in two different claims are not “substantively related,” thereby potentially averting the application of PHE under Colibri, the patentee may unwittingly fall into a trap of admitting that the elements are “alternatives,” and thus not equivalents under the DDD.

The strategy recommendation for patentees in view of both Colibri and the DDD remains unchanged. The Colibri court stated directly that “if Colibri wished to capture territory involving retraction . . . it could have filed a continuation application.”[9] If a separate patent is obtained on matter which was cancelled, that patent can be asserted directly rather than relying on a DOE theory. Where no such continuation application was filed or pursued, Colibri may complicate DOE arguments where applicable claim amendments were made during prosecution. Patentees should pursue potentially important claims in continuation or, if applicable, broadening reissue applications, and not rely on the DOE as a primary position when building a strong and enforceable patent portfolio.

[1] Colibri Heart Valve LLC v. Medtronic Corevalve LLC, No. 2023-2153, slip op. (Fed. Cir. July 18, 2025) (Precedential).

[2] See, e.g., Warner-Jenkinson Co. v. Hilton Davis Chem. Co., 520 U.S. 17 (1997).

[3] See generally, Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., 535 U.S. 722 (2002).

[4] Id. at 741.

[5] Colibri v. Medtronic, No. 2023-2153.

[6] See, U.S. Patent No. 8,900,294. Claim 1 thereof was asserted against Medtronic.

[7] Before its cancellation, claim 39 stood rejected under 35 U.S.C. § 112 for lack of written description. Claim 39 was subsequently cancelled and the rejection was withdrawn. Colibri v. Medtronic, No. 2023-2153, at *2.

[8] See, e.g., Eagle Pharmaceuticals Inc. v. Slayback Pharma LLC, 958 F.3d 1171 (2020).

[9] Colibri v. Medtronic, No. 2023-2153, at *24.