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SUPREME COURT OF THE UNITED STATES
_________________
No. 20–440
_________________
MINERVA SURGICAL, INC., PETITIONER
v.
HOLOGIC, INC., et al.
on writ of certiorari to the united states
court of appeals for the federal circuit
[June 29, 2021]
Justice Kagan delivered the opinion of the
Court.
In
Westinghouse Elec. & Mfg. Co. v.
Formica Insulation Co.,
266 U.S.
342, 349 (1924), this Court approved the “well settled”
patent-law doctrine of “assignor estoppel.” That doctrine, rooted
in an idea of fair dealing, limits an inventor’s ability to assign
a patent to another for value and later contend in litigation that
the patent is invalid. The question presented here is whether to
discard this century-old form of estoppel. Continuing to see value
in the doctrine, we decline to do so. But in upholding assignor
estoppel, we clarify that it reaches only so far as the equitable
principle long understood to lie at its core. The doctrine applies
when, but only when, the assignor’s claim of invalidity contradicts
explicit or implicit representations he made in assigning the
patent.
I
Inventors look to the patent system to obtain
valuable rights. A typical patent application, filed with the U. S.
Patent and Trademark Office (PTO), includes a written description
and drawing of the invention and one or more claims particularly
setting out the invention’s scope. See 35 U. S. C.
§§111–113. The application also usually contains an inventor’s
oath—a statement attesting that the applicant is “the original
inventor” of the “claimed invention,” so that he is entitled to the
patent sought. §115. If the PTO decides that the invention meets
the “conditions for patentability”—mainly, that the invention is
useful, novel, and non-obvious—it will issue a patent to the
inventor. See §§101–103. That award gives the inventor the right to
exclude others from making, using, or selling the invention until
the patent expires (currently, 20 years after the application
date). See §154.
The invention sparking this lawsuit is a device
to treat abnormal uterine bleeding, a medical condition affecting
many millions of women. Csaba Truckai, a founder of the company
Novacept, Inc., invented the device—called the NovaSure System—in
the late 1990s. He soon afterward filed a patent application, and
assigned his interest in the application—as well as in any future
“continuation applications”—to Novacept.[
1] The NovaSure System, as described in Truckai’s
patent application, uses an applicator head to destroy targeted
cells in the uterine lining. To avoid unintended burning or
ablation (tissue removal), the head is “moisture permeable,”
meaning that it conducts fluid out of the uterine cavity during
treatment. The PTO issued a patent, and in 2001 the Food and Drug
Administration (FDA) approved the device for commercial
distribution. But neither Truckai nor Novacept currently benefits
from the NovaSure System patent. In 2004, Novacept sold its assets,
including its portfolio of patents and patent applications, to
another company (netting Truckai individually about $8 million).
And in another sale, in 2007, respondent Hologic, Inc. acquired all
patent rights in the NovaSure System. Today, Hologic sells that
device throughout the United States.
Not through with inventing, Truckai founded in
2008 petitioner Minerva Surgical, Inc. There, he developed a
supposedly improved device to treat abnormal uterine bleeding.
Called the Minerva Endometrial Ablation System, the device (like
the NovaSure System) uses an applicator head to remove cells in the
uterine lining. But the new device, relying on a different way to
avoid unwanted ablation, is “moisture impermeable”: It does not
remove any fluid during treatment. The PTO issued a patent for the
device, and in 2015 the FDA approved it for commercial sale.
Meanwhile, in 2013, Hologic filed a continuation
application requesting to add claims to its patent for the NovaSure
System. Aware of Truckai’s activities, Hologic drafted one of those
claims to encompass applicator heads generally, without regard to
whether they are moisture permeable. The PTO in 2015 issued the
altered patent as requested.
A few months later, Hologic sued Minerva for
patent infringement. Minerva rejoined that its device does not
infringe. But more relevant here, it also asserted that Hologic’s
amended patent is invalid. The essential problem, according to
Minerva, is that the new, broad claim about applicator heads does
not match the invention’s description, which addresses their
water-permeability. See Defendant Minerva’s Opening Brief in
Support of Its Motion for Partial Summary Judgment in No.
15–cv–1031 (Del.), Doc. 300, pp. 8–9, 13–15; see also
Festo
Corp. v.
Shoketsu Kinzoku Kogyo Kabushiki Co.,
535 U.S.
722, 736 (2002) (“What is claimed by the patent application
must be the same” as what is described). In response, Hologic
invoked the doctrine of assignor estoppel. Because Truckai assigned
the original patent application, Hologic argued, he and Minerva
(essentially, his alter-ego) could not impeach the patent’s
validity. The District Court agreed that assignor estoppel barred
Minerva’s invalidity defense, and also ruled that Minerva had
infringed Hologic’s patent. See 325 F. Supp. 3d 507, 524–525,
532 (Del. 2018). At a trial on damages, a jury awarded Hologic
about $5 million.
The Court of Appeals for the Federal Circuit
mainly upheld the judgment, focusing on assignor estoppel. The
court first “decline[d] Minerva’s invitation to ‘abandon [that]
doctrine.’ ” 957 F.3d 1256, 1267 (2020). Citing both this
Court’s precedents and equitable principles, the court affirmed the
doctrine’s “continued vitality.”
Id., at 1268. An assignor,
the court stated, “should not be permitted to sell something and
later to assert that what was sold is worthless, all to the
detriment of the assignee.”
Id., at 1265. The assignor makes
an “implicit representation” that the rights “he is assigning
(presumably for value) are not worthless.”
Ibid. It would
“work an injustice,” the court reasoned, to “allow the assignor to
make that representation at the time of assignment (to his
advantage) and later to repudiate it (again to his advantage).”
Ibid. (quoting
Diamond Scientific Co. v.
Ambico,
Inc., 848 F.2d 1220, 1224 (CA Fed. 1988)). The court then
applied assignor estoppel to bar Truckai and Minerva from raising
an invalidity defense. Here, the court rejected Minerva’s argument
that because “Hologic broadened the claims” after “Truckai’s
assignment,” it would “be unfair to block Truckai (or Minerva) from
challenging the breadth of those claims.” 957 F. 3d, at 1268.
Relying on circuit precedent, the court deemed it “irrelevant that,
at the time of the assignment, the inventor’s patent
application[ ] w[as] still pending” and that the assignee “may
have later amended the claims” without the inventor’s input.
Ibid. (quoting
Diamond Scientific, 848 F. 2d, at
1226).
We granted certiorari, 592 U. S. ___
(2021), to consider the important issues raised in the Federal
Circuit’s judgment. Assignor estoppel, we now hold, is well
grounded in centuries-old fairness principles, and the Federal
Circuit was right to uphold it. But the court failed to recognize
the doctrine’s proper limits. The equitable basis of assignor
estoppel defines its scope: The doctrine applies only when an
inventor says one thing (explicitly or implicitly) in assigning a
patent and the opposite in litigating against the patent’s
owner.
II
Courts have long applied the doctrine of
assignor estoppel to deal with inconsistent representations about a
patent’s validity. The classic case (different in certain respects
from the one here) begins with an inventor who both applies for and
obtains a patent, then assigns it to a company for value. Later,
the inventor/assignor joins a competitor business, where he
develops a similar—and possibly infringing—product. When the
assignee company sues for infringement, the assignor tries to
argue—contrary to the (explicit or implicit) assurance given in
assigning the patent—that the invention was never patentable, so
the patent was never valid. That kind of about-face is what
assignor estoppel operates to prevent—or, in legalese, estop. As
one of the early American courts to use the doctrine held: The
assignor is not “at liberty to urge [invalidity] in a suit upon his
own patent against a party who derives title to that patent through
him.”
Woodward v.
Boston Lasting Mach. Co., 60 F.
283, 284 (CA1 1894). Or as the Federal Circuit held in modern
times: The assignor’s explicit or “implicit representation” that
the patent he is assigning is “not worth- less . . .
deprive[s] him of the ability to challenge later the [patent’s]
validity.”
Diamond Scientific, 848 F. 2d, at 1224.
Assignor estoppel got its start in late
18th-century England and crossed the Atlantic about a hundred years
later. In the first recorded case, Lord Kenyon found that a patent
assignor “was by his own oath and deed estopped” in an infringement
suit from “attempt[ing] to deny his having had any title to
convey.”
Oldham v.
Langmead (1789), as described in
J. Davies, Collection of the Most Important Cases Respecting
Patents of Invention and the Rights of Patentees 442 (1816); see
Hayne v.
Maltby, 3 T. R. 439, 441, 100 Eng. Rep. 665,
666 (K. B. 1789) (recognizing the
Oldham holding). That rule
took inspiration from an earlier doctrine—estoppel by deed—applied
in real property law to prevent a conveyor of land from later
asserting that he had lacked good title at the time of sale. See 2
E. Coke, The First Part of the Institutes of Laws of England 352a
(Hargrave & Butler eds., 19th ed. 1832) (1628). Lord Kenyon’s
new patent formulation of the doctrine grew in favor throughout the
1800s as an aspect of fair dealing: When “the Defendant sold and
assigned th[e] patent to the Plaintiffs as a valid one,” it “does
not lie in his mouth to say that the patent is not good.”
Chambers v.
Crichley, 33 Beav. 374, 376, 55 Eng. Rep.
412 (1864); see
Walton v.
Lavater, 8 C. B. N. S.
162, 187, 141 Eng. Rep. 1127, 1137 (C. P. 1860) (“The defendant,
who has received a large sum for the sale of this patent, ought not
to be allowed to raise any question as to its validity”). The
earliest American decision applying the doctrine dates from 1880.
See
Faulks v.
Kamp, 3 F. 898 (CC SDNY). Within a
decade or two, the doctrine was “so well established and generally
accepted that citation of authority is useless.”
Griffith v.
Shaw, 89 F. 313, 315 (CC SD Iowa 1893); see 2 W. Robinson,
Law of Patents for Useful Inventions §787 (1890) (collecting
cases).
This Court first considered—and unanimously
approved—assignor estoppel in 1924, in
Westinghouse v.
Formica. Speaking through Chief Justice Taft, the Court
initially invoked the doctrine’s uniform acceptance in the lower
courts. The first decision applying assignor estoppel, the Court
recounted, was soon “followed by a myriad.” 266 U. S., at 349.
“[L]ater cases in nearly all the Circuit Courts of Appeal” were “to
the same point” as the first, adding up to a full “forty-five years
of judicial consideration and conclusion.”
Ibid. Such a
“well settled” rule, in the Court’s view, should “not [be] lightly
disturb[ed].”
Ibid. And so it was not disturbed, lightly or
otherwise. Rather, the Court added its own voice to that
pre-existing “myriad.” We announced that an assignor “is estopped
to attack” the “validity of a patented invention which he has
assigned.”
Ibid. “As to the rest of the world,” the Court
explained, “the patent may have no efficacy”; but “the assignor can
not be heard to question” the assignee’s rights in what was
conveyed.
Ibid.
Westinghouse, like its precursor
decisions, grounded assignor estoppel in a principle of fairness.
“If one lawfully conveys to another a patented right,” the Court
reasoned, “fair dealing should prevent him from derogating from the
title he has assigned.”
Id., at 350. After all, the “grantor
purports to convey the right to exclude others”; how can he later
say, given that representation, that the grantee in fact possesses
no such right?
Ibid. The Court supported that view of equity
by referring to estoppel by deed. See
supra, at 6. Under
that doctrine, the Court explained, “a grantor of a deed of land”
cannot “impeach[ ] the effect of his solemn act” by later
claiming that the grantee’s title is no good.
Westinghouse,
266 U. S., at 350. “The analogy” was “clear”: There was “no
reason why the principles of estoppel by deed should not apply to
[the] assignment of a patent right.”
Id., at 348, 350. In
the latter context too, the Court held, the assignor could not
fairly “attack” the validity of a right he had formerly sold.
Id., at 349.
After thus endorsing assignor estoppel, the
Court made clear that the doctrine has limits. Although the
assignor cannot assert in an infringement suit that the patent is
invalid, the Court held that he can argue about how to construe the
patent’s claims. Here, the Court addressed the role in patent suits
of prior art—the set of earlier inventions (and other information)
used to decide whether the specified invention is novel and
non-obvious enough to merit a patent.
Id., at 350. “Of
course,” the Court said, the assignor cannot use prior art in an
infringement suit “to destroy the patent,” because he “is estopped
to do this.”
Id., at 351. But he can use prior art to
support a narrow claim construction—to “construe and narrow the
claims of the patent, conceding their validity.”
Id., at
350–351. “Otherwise,” the Court explained, a judge “would be
denied” the “most satisfactory means” of “reaching a just
conclusion” about the patent’s scope—a conclusion needed to resolve
the infringement charge.
Id., at 350–351. “The distinction”
thus established, the Court thought, “may be a nice one, but seems
to be workable.”
Id., at 351. And, indeed, the Court applied
it to decide the case at hand for the assignor, finding that he had
not infringed the properly narrowed claim.[
2]
Finally, the Court left for another day several
other questions about the contours of assignor estoppel. One
concerned privity: When was an assignor so closely affiliated with
another party that the latter would also be estopped? See
id., at 355. Another related to consideration: What if an
assignor had received only a nominal amount of money for
transferring the patent? See
ibid. But the question that
most interested the Court was whether estoppel should operate
differently if the assignment was not of a granted patent but of a
patent application—as in fact was true in that case. The Court saw
a possible distinction between the two. In a patent application,
the Court began, the inventor “swor[e] to” a particular
“specification.”
Id., at 352. But the exact rights at issue
were at that point “inchoate”—not “certainly defined.”
Ibid.
And afterward, the Court (presciently) observed, the claims might
be “enlarge[d]” at “the instance of the assignee” beyond what the
inventor had put forward.
Id., at 353. That might weaken the
case for estoppel. But the Court decided not to decide the issue,
given its holding that the assignor had not infringed the
(narrowed) patent claim anyway.
III
Minerva’s main argument here, as in the
Federal Circuit, is that “assignor estoppel should be
eliminated”—and indeed has been already. Brief for Petitioner 17.
We reject that view. The doctrine has lasted for many years, and we
continue to accept the fairness principle at its core. Minerva’s
back-up contention is that assignor estoppel “should be
constrained.”
Id., at 41. On that score, we find that the
Federal Circuit has applied the doctrine too expansively. Today, we
clarify the scope of assignor estoppel, including in the way
Westinghouse suggested.
A
In its quest to abolish assignor estoppel,
Minerva lodges three main arguments. The first two offer different
reasons for why the doctrine is already defunct: because Congress
repudiated it in the Patent Act of 1952 and because, even if not,
this Court’s post-
Westinghouse cases “leave no room for the
doctrine to continue.” Brief for Petitioner 20. The third, by
contrast, is a present-day policy claim: that assignor estoppel
“imposes” too high a “barrier to invalidity challenges” and so
keeps bad patents alive.
Id., at 38. (The principal dissent
essentially endorses the first two arguments, but not the third.
See
post, at 1, 4–6, 11 (opinion of Barrett, J.).)
On the first point, we do not agree that the
Patent Act of 1952 abrogated assignor estoppel. The statutory
language Minerva relies on provides that “[i]nvalidity” of the
patent “shall be [a] defense[ ] in any action involving”
infringement. 35 U. S. C. §282(b). According to Minerva,
that language “instructs that invalidity
must be available
as a defense in
every [infringement] action,” thus
“leav[ing] no room for assignor estoppel.” Brief for Petitioner
17–18 (emphasis in original). But to begin with, similar language,
entitling a defendant to plead invalidity in any infringement
action, was in the patent statute when
Westinghouse was
decided. See Patent Act of 1897, ch. 391, §2, 29Stat. 692 (“In any
action for infringement the defendant may plead” invalidity). And
anyway, Minerva’s view is untenable because it would foreclose
applying in patent cases a whole host of common-law preclusion
doctrines—not just assignor estoppel, but equitable estoppel,
collateral estoppel, res judicata, and law of the case. That broad
result would conflict with this Court’s precedents. See,
e.g.,
SCA Hygiene Products Aktiebolag v.
First
Quality Baby Products, LLC, 580 U. S. ___, ___ (2017)
(slip op., at 16) (recognizing equitable estoppel in a patent
suit). And it would subvert congressional design. For Congress
“legislate[s] against a background of common-law adjudicatory
principles,” and it “expect[s]” those principles to “apply except
when a statutory purpose to the contrary is evident.”
Astoria
Fed. Sav. & Loan Assn. v.
Solimino,
501 U.S.
104, 108 (1991) (internal quotation marks omitted). Assignor
estoppel was by 1952 just such a background principle of patent
adjudication, and Congress gave no indication of wanting to
terminate it or disturb its development. Nor has Congress done so
since that time.
We likewise do not accept Minerva’s view that
two of our post-
Westinghouse decisions have already interred
assignor estoppel. According to Minerva (quoting the case’s
dissent),
Scott Paper Co. v.
Marcalus Mfg. Co.
“eliminated any justification for assignor estoppel and
‘repudiated’ the doctrine.” Reply Brief 13 (quoting
326 U.S.
249, 264 (1945) (Frankfurter, J., dissenting)). And if that
were not enough, Minerva continues, our decision in
Lear,
Inc. v.
Adkins,
395 U.S.
653 (1969), also “eviscerated any basis for assignor estoppel.”
Reply Brief 13. But we think the words “eliminated,” “repudiated,”
and “eviscerated” are far off.
Scott Paper and
Lear
in fact retained assignor estoppel; all they did was police the
doctrine’s boundaries (just as
Westinghouse did and we do
today).
Whatever a worked-up dissent charged,
Scott
Paper did nothing more than decline to apply assignor estoppel
in a novel and extreme circumstance. The petitioner in
Scott
Paper made the same ask Minerva does here: to abolish the
Westinghouse rule. The Court expressly declined that
request. See 326 U. S., at 254. And it restated the “basic
principle” animating assignor estoppel, describing it as “one of
good faith, that one who has sold his invention may not, to the
detriment of the purchaser, deny the existence of that which he has
sold.”
Id., at 251. The Court, to be sure, declined to apply
the doctrine in the case before it. There, estoppel would have
prevented the assignor from making a device on which the patent had
expired—a device, in other words, that had already entered the
public domain. The Court could not find any precedent for applying
estoppel in that situation. See
id., at 254. And the Court
thought that doing so would carry the doctrine too far, reasoning
that the public’s interest in using an already-public invention
outweighs the “interest in private good faith.”
Id., at
256–257. But the Court did not question—again, it reaffirmed—the
principle of fairness on which assignor estoppel rests in more
common cases, where the assignee is not claiming to control a
device unequivocally part of the public domain. See
id., at
251. In those cases, the doctrine remained intact.
Lear gives Minerva still less to work
with. In that case, the Court considered and toppled a different
patent estoppel doctrine. Called licensee estoppel, it barred (as
its name suggests) a patent licensee from contesting the validity
of the patent on a device he was paying to use. Minerva’s basic
claim is that as goes one patent estoppel rule, so goes another.
Brief for Petitioner 23–25. But
Lear did not purport to
decide the fate of the separate assignor estoppel doctrine. To the
contrary, the Court stated that the patent holder’s “equities” in
the assignment context “were far more compelling than those
presented in the typical licensing arrangement.” 395 U. S., at
664. And so they are. As explained earlier, assignor estoppel rests
on the idea that the assignor has made an explicit or implicit
representation about the patent’s validity, and received some kind
of payment in return. See
supra, at 5–6. No rationale of
that kind supports licensee estoppel. The licensee is a buyer of
patent rights, not a seller. He has given no assurances of the
patent’s worth. All he has done is purchase the right to use a
patented device—which, if the patent is invalid, he need not have
done.
Lear’s refusal to bar a licensee’s claim of invalidity
showed that the Court was alert to “the important public interest
in permitting full and free competition in the use of ideas”—and so
would not always apply patent estoppel doctrines. 395 U. S.,
at 670. But that does not mean, at the other extreme, always
rejecting those doctrines.
Lear counseled careful attention
to the equities at stake in discrete patent contexts—and expressly
distinguished assignor from licensee estoppel.
In sum,
Scott Paper and
Lear left
Westinghouse right about where they found it—as a bounded
doctrine designed to prevent an inventor from first selling a
patent and then contending that the thing sold is worthless.
Westinghouse saw that about-face as unfair;
Scott
Paper and
Lear never questioned that view. At the same
time,
Westinghouse realized that assignor estoppel has
limits: Even in approving the doctrine, the Court made clear that
not every assignor defense in every case would fall within its
scope. See
supra, at 7–8.
Scott Paper and
Lear
adopted a similar stance. They maintained assignor estoppel, but
suggested (if in different ways) that the doctrine needed to stay
attached to its equitable moorings. The three decisions together
thus show not the doctrinal “eviscerat[ion]” Minerva claims, Reply
Brief 13, but only the kind of doctrinal evolution typical of
common-law rules.
Finally, we do not think, as Minerva claims,
that contemporary patent policy—specifically, the need to weed out
bad patents—supports overthrowing assignor estoppel. In rejecting
that argument, we need not rely on
stare decisis: “[C]orrect
judgments have no need for that principle to prop them up.”
Kimble v.
Marvel Entertainment, LLC, 576 U.S. 446,
455 (2015). And we continue to think the core of assignor estoppel
justified on the fairness grounds that courts applying the doctrine
have always given. Assignor estoppel, like many estoppel rules,
reflects a demand for consistency in dealing with others. See H.
Herman, The Law of Estoppel §3 (1871) (“An estoppel is an
obstruction or bar to one’s alleging or denying a fact contrary to
his own previous action, allegation or denial”). When a person
sells his patent rights, he makes an (at least) implicit
representation to the buyer that the patent at issue is valid—that
it will actually give the buyer his sought-for monopoly.[
3] In later raising an invalidity
defense, the assignor disavows that implied warranty. And he does
so in service of regaining access to the invention he has just
sold. As the Federal Circuit put the point, the assignor wants to
make a “representation at the time of assignment (to his advantage)
and later to repudiate it (again to his advantage).”
Diamond
Scientific, 848 F. 2d, at 1224; see
supra, at 4. By
saying one thing and then saying another, the assignor wants to
profit doubly—by gaining both the price of assigning the patent and
the continued right to use the invention it covers. That course of
conduct by the assignor strikes us, as it has struck courts for
many a year, as unfair dealing—enough to outweigh any loss to the
public from leaving an invalidity defense to someone other than the
assignor.[
4]
B
Still, our endorsement of assignor estoppel
comes with limits—true to the doctrine’s reason for being. Just as
we guarded the doctrine’s boundaries in the past, see
supra,
at 7–8, 11–13, so too we do so today. Assignor estoppel should
apply only when its underlying principle of fair dealing comes into
play. That principle, as explained above, demands consistency in
representations about a patent’s validity: What creates the
unfairness is contradiction. When an assignor warrants that a
patent is valid, his later denial of validity breaches norms of
equitable dealing. And the original warranty need not be express;
as we have explained, the assignment of specific patent claims
carries with it an implied assurance. See
supra, at 13. But
when the assignor has made neither explicit nor implicit
representations in conflict with an invalidity defense, then there
is no unfairness in its assertion. And so there is no ground for
applying assignor estoppel.
One example of non-contradiction is when the
assignment occurs before an inventor can possibly make a warranty
of validity as to specific patent claims. Consider a common
employment arrangement. An employee assigns to his employer patent
rights in any future inventions he develops during his employment;
the employer then decides which, if any, of those inventions to
patent. In that scenario, the assignment contains no representation
that a patent is valid. How could it? The invention itself has not
come into being. See Lemley, Rethinking Assignor Estoppel, 54
Houston L. Rev. 513, 525–527 (2016). And so the employee’s
transfer of rights cannot estop him from alleging a patent’s
invalidity in later litigation.
A second example is when a later legal
development renders irrelevant the warranty given at the time of
assignment. Suppose an inventor conveys a patent for value, with
the warranty of validity that act implies. But the governing law
then changes, so that previously valid patents become invalid. The
inventor may claim that the patent is invalid in light of that
change in law without contradicting his earlier representation.
What was valid before is invalid today, and no principle of
consistency prevents the assignor from saying so.
Most relevant here, another post-assignment
development—a change in patent claims—can remove the rationale for
applying assignor estoppel.
Westinghouse itself anticipated
this point, which arises most often when an inventor assigns a
patent application, rather than an issued patent. As
Westinghouse noted, “the scope of the right conveyed in such
an assignment” is “inchoate”—“less certainly defined than that of a
granted patent.” 266 U. S., at 352–353; see
supra, at
9. That is because the assignee, once he is the owner of the
application, may return to the PTO to “enlarge[ ]” the
patent’s claims. 266 U. S., at 353; see 35 U. S. C.
§120; 37 CFR §1.53(b). And the new claims resulting from that
process may go beyond what “the assignor intended” to claim as
patentable. 266 U. S., at 353.
Westinghouse did not
need to resolve the effects of such a change, but its liberally
dropped hints—and the equitable basis for assignor estoppel—point
all in one direction. Assuming that the new claims are materially
broader than the old claims, the assignor did not warrant to the
new claims’ validity. And if he made no such representation, then
he can challenge the new claims in litigation: Because there is no
inconsistency in his positions, there is no estoppel. The limits of
the assignor’s estoppel go only so far as, and not beyond, what he
represented in assigning the patent application.
The Federal Circuit, in both its opinion below
and prior decisions, has failed to recognize those boundaries.
Minerva (recall, Truckai’s alter-ego) argued to the court that
estoppel should not apply because it was challenging a claim that
was materially broader than the ones Truckai had assigned. But the
court declined to consider that alleged disparity. Citing circuit
precedent, the court held it “irrelevant” whether Hologic had
expanded the assigned claims: Even if so, Minerva could not contest
the new claim’s validity. 957 F. 3d, at 1268 (quoting
Diamond Scientific, 848 F. 2d, at 1226); see
supra, at 4. For the reasons given above, that conclusion is
wrong. If Hologic’s new claim is materially broader than the ones
Truckai assigned, then Truckai could not have warranted its
validity in making the assignment. And without such a prior
inconsistent representation, there is no basis for estoppel.
We remand this case to the Federal Circuit to
now address what it thought irrelevant: whether Hologic’s new claim
is materially broader than the ones Truckai assigned. The parties
vigorously disagree about that issue. In Truckai’s view, the new
claim expanded on the old by covering non-moisture-permeable
applicator heads. In Hologic’s view, the claim matched a prior one
that Truckai had assigned. Resolution of that issue in light of all
relevant evidence will determine whether Truckai’s representations
in making the assignment conflict with his later invalidity
defense—and so will determine whether assignor estoppel
applies.
IV
This Court recognized assignor estoppel a
century ago, and we reaffirm that judgment today. But as the Court
recognized from the beginning, the doctrine is not limitless. Its
boundaries reflect its equitable basis: to prevent an assignor from
warranting one thing and later alleging another. Assignor estoppel
applies when an invalidity defense in an infringement suit
conflicts with an explicit or implicit representation made in
assigning patent rights. But absent that kind of inconsistency, an
invalidity defense raises no concern of fair dealing—so assignor
estoppel has no place.
For these reasons, we vacate the judgment of the
Federal Circuit and remand the case for further proceedings
consistent with this opinion.
It is so ordered.