Supreme Court will hear Assignor Estoppel Case

Minerva Surgical Inc. v. Hologic Inc. (Supreme Court 2021)

The Supreme Court has granted certiorari in this case involving the traditional doctrine of assignor estoppel.

Question Presented by Minerva: The question is whether a defendant in a patent infringement action who assigned the patent, or is in privity with an assignor of the patent, may have a defense of invalidity heard on the merits.

Question Presented by Hologic: The question presented is whether the longstanding common-law doctrine of assignor estoppel should be abrogated by this Court.

Petition for Writ of CertiorariOpposition to CertiorariReply Brief;
Amicus by IP Professors (Lemley) – Engine Advocacy.

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The appellate panel in the case upheld the doctrine of assignor estoppel, but also found that an assignor could collaterally attack via IPR since the PTO does not enforce the doctrine.  The panel – led by Judge Stoll — also called for reconsideration of the doctrine “as it applies both in district court and in the Patent Office.”

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There are several related doctrines here: Estoppel by Deed, Assignor Estoppel; Licensee Estoppel. Licensee estoppel in the patent context was ended by Lear v. Adkins, 395 U.S. 653 (1969).  Prior to the Federal Circuit, some courts expanded Lear to also eliminate Assignor Estoppel.  See., e.g., Coastal Dynamics Corp. v. Symbolic
Displays, Inc., 469 F.2d 79 (9th Cir. 1972) (per curiam).  However, the Federal Circuit did not agree and has applied assignor estoppel over the decades to bar validity challenges by inventors and prior owners who are later sued for infringement.  While licensee estoppel is contract focused, its property law parallel is estoppel by deed which bars a prior-owner from “denying the truth of the deed.” Estoppel by deed servers as the doctrinal foundation for assignor estoppel in patent law.  Assignor estoppel is seemingly strengthened because the patent applicant publicly assures the USPTO of the patent’s validity by claiming patent rights.

In the end though, I believe that assignor estoppel only creates a strong presumption.  I expect that no estoppel would apply in cases where the seller expressly reserves the right to later challenge the patent. Of course, most employee-inventors will not have the negotiation power or awareness to demand such a provision.

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24 thoughts on “Supreme Court will hear Assignor Estoppel Case

  1. 3

    Dennis, this is thinking some more about your “I expect that no estoppel would apply in cases where the seller expressly reserves the right to later challenge the patent. ” [Patent assignments other than by employees.]
    I wonder if an effective yet more easily agreed to alternative to avoid assignor estoppel would be the sale of the patent with an express disclaimer of any warranties (of validity, enforceability, fitness for purpose, etc.) [i.e., effectively a “quit claim deed” to the patent] [which I saw on occasion]?

    1. 3.1

      I do not think that such would reach the underlying issue of the original inventor’s oath.

      That oath is NOT a part of any later business deal or contract and does not become a leverage point that can be ‘negotiated away.’

      And it shouldn’t be.

  2. 1

    Re Minerva Surgical Inc. v. Hologic Inc. – Supreme Court cert granted on patent assignor estoppel. Glad this finally got to the Sup. Ct.
    Dennis, good point about employed inventor assignments, since those are the vast majority of all patent assignments. And employed inventors of course normally do not do prior art searches if they do not own the invention.
    I’m curious if it will be argued that this equitable doctrine blocks departing employees from starting new and competitive companies even by invalid patents? [Noting that commentators here argue there is already a serious problem with trade secret laws.] Also, the Sup. Ct. does not seem fond of other non-statutory patent equitable estoppels like “laches” lately.
    On the other hand, inventors should not be able to easily deny the truth of their executed inventorship declaration, which is under oath.
    Which suggests a possible [if unlikely] compromise decision? Retain patent assignor estoppel for invalidity assertions based on evidence the inventor was or should have been aware of at their inventorship declaration date, but no estoppel for invalidity evidence not discovered until after the patent issued.

    1. 1.1

      BTW I think this is a well written cert petition for an advantageously “bad facts” case. It argues that here “The Federal Circuit expanded assignor estoppel in this case to bar petitioner Minerva from raising invalidity defenses that arose only because the ultimate assignee of the patent rights, respondent Hologic, had broadened the scope of the patent beyond anything the inventor had claimed. Minerva’s invalidity defense was based solely on Section 112’s written description and enablement requirements. The Federal Circuit had never before applied assignor estoppel to that kind of invalidity defense, and there is no reason why it should.”

      1. 1.1.1

        Note that employee inventors typically have no control over the prosecution of their patent applications. I myself uncovered in an interference one time that the opponent’s inventor had not agreed to filing claims he considered too broad in view of known prior art. They were added later by amendment without his permission and he was fired.


          This though IS a legitimate gripe.

          Inventors — and others involved — have an ongoing duty throughout prosecution, and that duty is necessarily involved with claim scope, especially amended claim scope.

          Of course, ANY amended claim scope can also be said to be included with the application AS FILED given that the US does have a “no new matter” rule, and a proper treatment of an improperly broad amended claim scope would (or should) be first indicated in a new matter rejection.


          “I myself uncovered in an interference one time that the opponent’s inventor had not agreed to filing claims he considered too broad in view of known prior art.”

          I discuss claim amendments/new claims with inventors all the time. I don’t regard their opinions on novelty, non-obviousness, support, etc. to be “binding” on me in any way. If the claims are, in my opinion, supported, enabled, clear and definite, novel, and non-obvious over the known prior art, and they would be valuable to the client then I’m going to file them.


            Of course, and perfectly reasonable (seeing as the oath that ALL inventors provide goes beyond merely the claims and covers the entirety of the filed application.

            As noted, any amendment thus made during prosecution that falls within the other legal bounds is most definitely fair game.


              I have worked for clients that request/require supplemental oaths/declarations in any allowed cases where the final claims differ in scope from the originally filed claims. It’s up to the clients. My personal professional opinion is that such is not required. But others have different opinions.

      2. 1.1.2

        The assertion of a later assignee “expanding” anything is pure bunk and is not in fact a good example of anything except a sanctionable offense.


          I’m curious how many readers here agree with anon’s assertion above that employer-assigned application claims are never broadened by amendment after filing, or that patent claims cannot be broadened in a broadening reissue application by an assignee?


            … your response contains an (obvious) fallacy, Paul – see my comment above.

            It has been awhile for you since your prosecution days, hasn’t it been?


                LOL – do you ever get tired of picking the 180 degree off track posts to assert the wrong thing?

                Beep Beep!


            Also, please point out the alleged language in the inventor application oath or declaration limiting claim scope to original claims? 35 USC 115(b)


              You appear to be confused here Paul, and I am the one that is to be asking you to show why the oath must be limited to claim scope of only originally filed claims.

              Your request here indicates that you want me to vouch for a position that I have not advocated. Your reference actually makes my point for me.


            An assertion that has no place in fact of an expansion of scope beyond that which an inventor has already provided their oath to.

            Note that an oath is NOT just to the claims as filed, but to the entire contents of the as-filed application.

            A mere amendment that broadens is simply not a proper justification for someone who has taken an oath to later (when advantages have changed) to renege on that oath.

            If a case of ‘new matter’ can not also be maintained, the assertion is baseless. Baseless assertions are sanctionable.

            (I do note that there are additional nuances involved, especially for patents to which there are multiple inventors)

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