To recap, the case arose in an infringement suit over U.S. Patent Nos. 6,782,183 and 9,095,348.  The patents were directed to "procedures and devices for endometrial ablation."  Claim 9 of the '183 patent and claim 1 of the '348 patent were considered by the Court to be representative:

'183 patent:

9.  A method of detecting a perforation in a uterus, comprising the steps of:
passing an inflation medium into the uterus;
    monitoring for the presence of a perforation in the uterus using a pressure sensor;
    if no perforation is detected during the monitoring step, permitting ablation of the uterus using an ablation device; and
    if a perforation is detected during the monitoring step, preventing ablation of the uterus.

'348 patent:

1.  A device for treating a uterus comprising:
an elongate member having a proximal portion and a distal portion, the elongate member comprising
    an outer sleeve and an inner sleeve slidably and co-axially disposed within the outer sleeve;
    an applicator head coupled to the distal portion, the applicator head defining an interior volume and having a contracted state and an expanded state, the contracted state being configured for transcervical insertion and the expanded state being configured to conform to the shape of the uterus, the applicator head including one or more electrodes for ablating endometrial lining tissue of the uterus;
    a handle coupled to the proximal portion of the elongate member, wherein the handle comprises a frame, a proximal grip and a distal grip pivotally attached to one another at a pivot point and operably coupled to the applicator head so that when the proximal grip and the distal grip are moved closer together, the applicator head transitions from the contracted state to the expanded state;
    a deflecting mechanism including flexures disposed within the applicator head, the flexures including first and second internal flexures and first and second external flexures, the first and second external flexures being coupled to the outer sleeve and the first and second internal flexures being coupled to the inner sleeve, wherein the deflecting mechanism is configured so that translating the inner sleeve relative to the frame causes the applicator head to transition from the contracted state to the expanded state; and
    an indicator mechanism operably coupled to the inner sleeve, the indicator mechanism configured to indicate a dimension of the uterus [emphases added to indicate disputed claim terms not further discussed herein].

As set forth in the Federal Circuit's earlier opinion, inventor Truckai (named on both the '183 and '348 patents) founded Novocept, which developed a system for detecting perforations in a uterus that could cause serious side effects for women undergoing endometrial ablation; the system depends on introducing carbon dioxide into the uterus and monitoring gas escape.  It was undisputed that Novocept's ablation product uses the claimed technology, and that inventor Truckai assigned his right to these patents to Novocept.  Thereafter, Novocept was acquired by co-plaintiff Cytyc Corp., which was subsequently acquired by co-plaintiff Hologic.

Thereafter, Inventor Truckai founded accused infringer Minerva and developed the accused infringing article, termed the Endometrial Ablation System (EAS).  Hologic sued Minerva over sales of the EAS for infringing the '183 and '348 patents.  Hologic moved for summary judgment that Minerva was estopped from challenging the validity of both the '183 and '348 patents under the doctrine of assignor estoppel, which motion the District Court granted.  Minerva appealed the District Court's grant of summary judgment and the Federal Circuit affirmed; see Hologic, Inc v Minerva Surgical, Inc. (Fed. Cir. 2020)".

In vacating this judgment, the Supreme Court ruled 5-4 that while remaining viable the doctrine was limited to those instances where the assignor could be fairly understood to have warranted (either expressly or implicitly) the validity of the claims ultimately issued.  Thus, in many circumstances -- such as when an inventor assigns rights to a patent application that ultimately issues with significantly broader claims -- the doctrine should not apply.  In the case at bar, the Court recognized that Minerva's device worked in a different manner that the original device disclosed in the putatively infringed patent (including a moisture-impermeable head Minerva argued was not within the scope of the assigned claims).  Hologic (the successor-in-interest), had filed a continuation of the original application and pursued claims that would encompass devices regardless of the moisture permeability of the head; these claims issued and were the basis for the suit.  Because the Supreme Court understood that under these circumstances it could be unfair to the assignor to attribute assignment of such claims to result in the estoppel the Court vacated the judgment for reconsideration by the Federal of these factors.

The Federal Circuit once again affirmed the District Court's application of the assignor estoppel doctrine, in an opinion by Judge Stoll joined by Judges Clevenger and Wallach.  The Court framed the issue as whether the claims at issue were "materially broader" than the claims assigned to Hologic at the time of the assignment.  In doing so, the opinion set forth in brief what was disclosed in the specification and provides this comparison between claim 1 of the later-filed (i.e., post-assignment) '348 patent and claim 31 of continuation application no. 09/103,072 (which inventor Truckai assigned to Hologic's predecessor-in-interest).

This comparison provides the basis for the Federal Circuit's analysis of whether claim 1 of the '348 patent-in-suit is materially broader than claim 31 of the '072 application (regarding which it was undisputed that inventor Truckai assigned and would be subject the assignor estoppel).  The basis for Minerva's contention of material differences in breadth was that all assigned claims in the '072 patent expressly recited a moisture-permeable head, and while conceding claim 31 did not contain such a limitation maintained that this claim had been cancelled prior to the assignment and was not pending (and thus not within the scope of the assignment).  Hologic responded to this assertion by noting that cancellation of claim 31 during prosecution was "without prejudice" (pursuant to a restriction requirement) and thus that applicant had retained the right to pursue the claim in a related, later-filed application claiming priority to the '072 application.

In performing its analysis, the panel first addressed whether claim 31 was part of the inventor Truckai's assignment (thus providing a warranty as to its validity).  The Court considered this question in light of what an "objective assignee" would understand from the prosecution history and the reason(s) claim 31 had been cancelled.  In reviewing the prosecution history of the '072 application, the opinion notes that inventor Truckai successfully argued against an anticipation rejection against claim 31 and obtained an allowance, after which the Examiner applied the restriction requirement leading to cancellation of this claim.  Under these circumstances, the Federal Circuit held that there was no concession, implicit or explicit, regarding the patentability of claim 31.  ("Put another way, Mr. Truckai canceled claim 31 for reasons other than patentability.")  The objective assignee would have recognized, the Court concluded, that applicant had retained the right to prosecute claim 31 (and the other non-elected claims) in a future 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").  As stated in the opinion, "[a] claim canceled in response to a restriction requirement thus travels with the application."  Accordingly, the Court disagreed with Minerva's argument and held that claim 31 was both capable and was in fact assigned along with the rest of inventor Truckai's patent estate (the Court noting that the assignment included "the rights to any continuation, continuation-in-part, or divisional patent applications not yet filed").  This coupled with inventor Truckai's oath when the application was filed and representations in the assignment of having "'no present knowledge from which it could reasonably conclude' that these assigned intellectual property rights were invalid or unenforceable" as sufficient to satisfy an objective assignee's reliance that claim 31 was not invalid.

Turning to the task set forth by the Supreme Court, the panel considered whether claim 1 of the '348 patent was materially broader than claim 31 of the '072 application.  The opinion states that the parties have agreed that this question would be answered by the Court's consideration of only these two claims and a determination of whether there was a difference between moisture-permeable and moisture-impermeable devices.  (In a footnote the panel disclaims any wider consideration of the differences between "broader" claims and "materially broader" claims.)  The opinion sets forth the basis for its decision, wherein "if claim 31 is limited to moisture-permeable devices, the parties agree that claim 1 is 'materially broader' and assignor estoppel would not bar Minerva from asserting its invalidity defenses" (the Court already having construed claim 1 of the '348 patent to encompass moisture-permeable and moisture-impermeable embodiments of the claimed device).  In performing its assessment, the opinion states that the parties agree the "plain meaning" of claim 31 is not limited to moisture-impermeable devices (i.e., it is broad enough to encompass moisture-permeable devices as well).

In its construction the panel rejected Minerva's argument that claim 31 is missing a limitation to an "applicator head," stating that use of the open-ended term "comprising" actually supports devices comprising both moisture-permeable and -impermeable applicator heads.  The Court also rejected Minerva's argument that the term "electrode array" recited in claim 31 mandated the term to mean a moisture-permeable electrode array because the intrinsic evidence does not support this construction.  On the contrary, the Court states that the principle of claim differentiation supports the opposite conclusion, because claims 1 and 16 of the '072 application had expressly recited a moisture-permeable electrode array.  This showed that "Mr. Truckai and the other inventors knew how to draft claims that require moisture permeability" and "[t]he fact that they chose not to include this limitation in claim 31, unlike claims 1 and 16, indicates that they did not intend to so limit that claim," according to the Court.  And the opinion states that written description was not consistent with moisture permeability being "required or mandatory" and "it is improper to restrict claim 31 to this 'preferable' characteristic," citing Comaper Corp. v. Antec, Inc., 596 F.3d 1343, 1348 (Fed. Cir. 2010), and InterDigital Commc'ns, LLC v. Int'l Trade Comm'n, 690 F.3d 1318, 1328 (Fed. Cir. 2012).

The opinion concludes by noting that, Minerva not having disputed any of the "pertinent facts" relevant to whether assignor estoppel could be applied (other than the claim scope question), the Court reaffirmed its earlier determination that the District Court did not abuse its discretion in finding Minerva estopped from challenging the validity of the '348 patent on assignor estoppel grounds, and reinstated its earlier judgment on other appealed issues not affected by the Supreme Court's decision.

Hologic, Inc. v. Minerva Surgical, Inc. (Fed. Cir. 2022)
Panel: Circuit Judges Stoll, Clevenger, and Wallach
Opinion by Circuit Judge Stoll