In a move that whets the appetite of patent licensing nerds everywhere and is likewise surprising for a court not composed of such, the Supreme Court took up a case related to what the Federal Circuit described as "assignor estoppel"-the ability of a patentee that has assigned the rights of patents to challenge the validity of them after getting sued for infringement. The patents are related to endometrial ablation, a treatment wherein the uterus' lining is destroyed to treat menorrhagia—abnormally heavy menstrual bleeding.
The procedural history of the infringement case that lead to this situation is a bit confusing, so bear with me. In 1993, Csaba Truckai co-founded NovaConcept, Inc. and developed a medical device that ultimately received FDA approval in 2001. Truckai assigned his rights to the patents to NovaConcept in 1998. In 2004, Cytic Corporation acquired NovaConcept, which was acquired by Hologic in 2007. The patents at issue in the infringement were continuations off of Truckai's original application issued in 2004 and 2013 (respectively, Patent Nos. 6,872,183 and 9,095,348, or the '183 patent and the '348 patent). In 2008, Truckai left NovaConcept and founded Minerva, which developed an Endometrial Ablation System (EAS) that received FDA approval in 2015.
In November 2015, Hologic sued Minerva for infringement based on its EAS. Minerva raised a series of validity challenges against both the '183 and the '348 patents (ultimately invalidating the '183 patent in an Inter Partes Review (IPR) on obviousness grounds). However, when Minerva requested that the court moot the infringement claims under the '183 patent, the district court refused, noting that the IPR was on appeal and that the patent had not yet been canceled. Around the same time, Hologic moved for summary judgment that the doctrine of assignor estoppel barred Minerva from challenging the validity of the patents since Truckai had assigned the patents to NovaConcept. The district court ultimately granted summary judgment as to assignor estoppel and infringement of both patents, and the jury ultimately awarded Hologic $4,787,668.23 in damages. While the United States Court of Appeals for the Federal Circuit (CAFC) ultimately affirmed the obviousness finding of the IPR, the district court did not alter the jury award except to added prejudgment interest, postjudgment interest, and supplemental damages of $1,629,304.08. Both parties ultimately appealed aspects of the final judgment (Minerva challenged the estoppel, claim construction, and the jury's damages award, and Hologic challenged the supplemental damages award). But this article will focus on the aspect of assignor estoppel.
Assignor Estoppel, Licensee Estoppel, and the Lear Doctrine
In 1988, the CAFC defined assignor estoppel as "an equitable doctrine that prevents one who assigned the rights to a patent (or patent application) from later contending that what was assigned is a nullity."1. It noted that the estoppel effect applied to other parties in privity with the assignor (including a corporation founded thereby). It noted that certain earlier cases had carved out exceptions to the doctrine but had not abolished it. Importantly, it concluded that the landmark decision in Lear v. Adkins, which abolished a similar doctrine, licensee estoppel, did not apply in this instance,2 noting that unlike in Lear in which the licensee was obliged to continue paying royalties, the assignor in this Diamond Scientific had already been paid in full for the transfer of patent rights.3
Taking a Step Back: Licensee Estoppel and Lear
Before we continue discussing assignor estoppel, let's discuss the concept of licensee estoppel and how it came about. Licensee estoppel is a judge-made doctrine based on the idea that a licensee should not be able to "enjoy the benefit afforded by the agreement while simultaneously urging the patent which forms the basis of the agreement is void."4 The court in Lear abolished this notion, acknowledging the public policy encouraging people to challenge potentially invalid patents and the potential repression of competition that could be caused by the enforcement of "worthless patents."5 These notions of challenging "bad patents" have been particularly pervasive in the 21st-Century and seem to have firmly supplanted any concern that was previously held that licensees were taking advantage of the licensors by challenging such patents.
Back to Assignor Estoppel
While the court in Diamond Scientific acknowledged the effect of Lear, it found four justifications for nonetheless applying assignor estoppel: "(1) to prevent unfairness and injustice; (2) to prevent one [from] benefiting from his own wrong; (3) by analogy to estoppel by deed in real estate; and (4) by analogy to a landlord-tenant relationship."6 The CAFC also emphasized the underlying reasoning that an assignor "should not be permitted to sell something and later to assert that what was sold is worthless."
While the CAFC reiterated its reasoning in Diamond, it also noted some exceptions that had come up in past cases, including estoppel of patentees from asserting a previously invalidated patent and that an estopped assignor "may  argue for a narrow claim construction, or that the accused devices are within the prior art and therefore cannot infringe."7 The first argument does not really make much sense in the context of this case since assignor estoppel would have presumably prevented the IPR that the invalidity was based, but the second argument is basically saying that Minerva can challenge the infringement assertion by saying that its accused device was not subject to the rights of the assigned patent and that the interpretation adopted by the patentee rendered the claims invalid. Regarding the first point, the CAFC acknowledged that the result seemed unfair to Hologic but that the plain meaning of 35 U.S.C. Section 311(a) provides that "a person who is not the owner of a patent" may file an IPR overrode the effect of assignor estoppel in the context of IPRs.8
It should be noted at this point that the entire AIA scheme for administering IPRs is under question by a case that the Supreme Court will be hearing oral argument for on March 1, 2021 (Arthrex Inc. v. Smith & Nephew Inc.). There have been numerous procedural oddities that have resulted from the administrative post-grant proceedings promulgated by the America Invents Act (the AIA). The Supreme Court may use this case as a vehicle to further symmetrize the proceedings with their federal court counterparts.
 Diamond Scientific Co. v. Ambico, Inc., 848 F.2d 1220 (Fed. Cir. 1988).
 Lear v. Adkins, 395 U.S. 653 (1969).
 Diamond Scientific, 848 F.2dat 1223-24.
 Lear, 395 U.S. 653 at 656.
 Id. at 663-64.
 Diamond Scientific, 848 F.2d at 1224 (quoting Cooper, Estoppel to Challenge Patent Validity: The Case of Private Good Faith vs. Public Policy, 18 Case W. Res. L. Rev. 1122 (1967)).
 Westinghouse Electric & Manufacturing Co. v. Formica Insulation Co., 266 U.S. 342, 351 (1924).
 Arista Networks Inc. v. Cisco Sys., Inc., 908 F.3d 792, 802-04.