by Dennis Crouch
The defense of assignor estoppel has been in flux. The Federal Circuit had previously broadly applied the non-statutory doctrine to prevent a prior owner of patent rights (the “assignor”) from later challenging the validity of those rights. The basic idea was that the assignment of rights includes an implicit warranty. In a 2021 decision, the Supreme Court shrunk the doctrine by creating important caveats. Minerva Surgical, Inc. v. Hologic, Inc., 141 S. Ct. 2298 (2021). Although the Court retained the doctrine generally, it concluded that assignor estoppel is limited to situations where “the assignor’s claim of invalidity contradicts explicit or implicit representations made in assigning the patent.” Id. The court noted potential situations of no-estoppel: (1) assignment made prior to the inventor even seeing the patent document; (2) a change in the law that renders the patent invalid; and (3) after the assignment, the new owner changes the scope of the patent claims that goes “beyond what the assignor intended to claim as patentable.” A key example of this would be claim changes that result in scope that is “materially broader” than those originally assigned.
On remand, the Federal Circuit concluded that estoppel still applies despite the Supreme Court’s added limitations. Hologic, Inc. v. Minerva Surgical, Inc., 19-2054, — F.4th — (Fed. Cir. 2022). In particular, the appellate court found that the claims at issue in the litigation are not materially broader than what the assignor intended to claim at the time of the assignment.
The invention here relates to “an endometrial ablation device used to treat abnormal uterine bleeding (menorrhagia) by destroying targeted cells in the lining of the uterus.” Slip Op. The invention generally proposed use of a “fluid permeable elastic member” for moisture removal; except that one claim in the application did not require the use of the permeable member. (Claim 31).
Prior to the assignment at issue, the examiner had a restriction requirement and the patentee cancelled Claim 31 so that all of the remaining claims required the permeable member. The patent application was in this state — with only permeable member claims — when the assignment at issue took place. Later, the patentee obtained a patent covering the invention without the permeable member and then sued the assignor who had formed a competing company. In the litigaiton, the defendant challenged the broader claims as lacking written description, but the district court barred those challenges.
On appeal, the Federal Circuit found that in this context, the cancelled claim should still be considered part of the invention that the assignor expected to be patented.
[T]his 2002 cancelation in response to the Examiner’s restriction requirement says nothing, implicitly or explicitly, about the patentability of claim 31. Put another way, Mr. Truckai canceled claim 31 for reasons other than patentability. Indeed, an assignee would have understood that the restriction requirement and subsequent cancelation in response to the restriction requirement meant that the patent applicant could later prosecute claim 31’s subject matter. . . . Although claim 31 was canceled for purposes of further prosecution of the ’072 application, cancelation did not nullify the claim, as it remained viable for further prosecution in a divisional application filed by whomsoever owned the ’072 application. . . . The 2004 assignment assigned not just the rights to the ’072 application, but also the rights to any continuation, continuation-in-part, or divisional patent applications not yet filed. For certain, canceled claim 31 traveled with the ’072 application and its assignment to Hologic.
Slip Op. Thus, to understand changes in the patent claims, the court will delve into the prosecution history to uncover the reasons for any changes to claim scope and then make some conclusions about whether those reasons fit within the assignor’s implicit intent-to-claim. In a footnote, the opinion reserves the particulars for another day:
Our holding in this regard is limited to the facts of this case. We do not address whether a claim canceled for reasons other than to comply with a restriction requirement would be part of the 2004 assignment.
Slip Op., Note 4.
I’ll note that the facts of Hologic do not reflect an ordinary patent case. The assignment at issue was part of a $300 million company sale and thus was highly lawyered. The assignment particularly included an express warranty that the IP rights being assigned were both valid and enforceable. In the ordinary case, the inventor will be assigning rights to their employer pre-filing without the particular warranty or level of knowledge.