Court Opinion

ID: 4585168
Source: CourtListenerOpinion
Date Created: 2020-11-10 16:01:40.237391+00
Date Added: 2024-06-11T13:47:34.550437
License: Public Domain

Case: 20-1098    Document: 40     Page: 1   Filed: 11/10/2020

   United States Court of Appeals
       for the Federal Circuit
                  ______________________

   FERRING B.V., FERRING INTERNATIONAL
 CENTER SA, FERRING PHARMACEUTICALS INC.,
              Plaintiffs-Appellants

                             v.

     ALLERGAN, INC., ALLERGAN USA, INC.,
    ALLERGAN SALES, LLC, SEYMOUR H. FEIN,
             RONALD V. NARDI,
                 Defendants

 SERENITY PHARMACEUTICALS CORPORATION,
 SERENITY PHARMACEUTICALS, LLC, REPRISE
         BIOPHARMACEUTICS, LLC,
             Defendants-Appellees
            ______________________

                        2020-1098
                  ______________________

    Appeal from the United States District Court for the
 Southern District of New York in No. 1:12-cv-02650-PKC,
 Senior Judge P. Kevin Castel.
                  ______________________

                Decided: November 10, 2020
                  ______________________

     MARY W. BOURKE, Womble Bond Dickinson (US) LLP,
 Wilmington, DE, argued for plaintiffs-appellants. Also rep-
 resented by KRISTEN HEALEY CRAMER, DANA KATHRYN
 SEVERANCE; JOHN W. COX, JOSHUA A. DAVIS, Atlanta, GA.
Case: 20-1098    Document: 40         Page: 2      Filed: 11/10/2020

 2                                 FERRING B.V.   v. ALLERGAN, INC.

      SARAH ELIZABETH SPIRES, Skiermont Derby LLP, Dal-
 las, TX, argued for defendants-appellees. Also represented
 by PAUL SKIERMONT.
                   ______________________

     Before O’MALLEY, REYNA, and CHEN, Circuit Judges.
 O’MALLEY, Circuit Judge.
      When a district court enters judgment at the summary
 judgment stage, it is at times difficult to discern on appeal
 whether the nonmovant failed to raise sufficient factual
 disputes to prevent judgment or the court acted despite
 such disputes. Where the matter adjudged is a quintessen-
 tially fact-laden one, such as the equitable matter at issue
 here, it is especially important that we guard against a
 rush to judgment. We conclude that such a rush to judg-
 ment happened here. Accordingly, we vacate and remand
 for further development of the record and a later-stage res-
 olution of whether Appellants are equitably estopped from
 seeking to correct inventorship of the patents at issue in
 these proceedings.
                        BACKGROUND
                               I
     Seymour Fein worked as a consultant for Ferring Phar-
 maceuticals Inc. from December 1998 until the company
 terminated his consulting agreement on November 7, 2002.
 While Fein was consulting for Ferring Pharmaceuticals
 Inc., he became involved in a Ferring 1 project involving
 desmopressin. Desmopressin is a synthetic analog of the
 naturally occurring hormone arginine vasopressin, which

     1    We refer collectively to Appellants Ferring B.V.,
 Ferring International Center SA, and Ferring Pharmaceu-
 ticals Inc. collectively as “Ferring.”
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 FERRING B.V.   v. ALLERGAN, INC.                           3

 regulates the body’s retention of water. Among other
 things, desmopressin is used to treat nocturia (disruption
 of nighttime sleep due to the need to urinate).
     As early as 1999, Ferring scientists Jens Peter
 Nørgaard and Thomas Senderovitz were involved in a clin-
 ical trial studying the bioavailability and pharmacokinet-
 ics of desmopressin. The trial demonstrated that orally
 administered desmopressin had a duration of action in the
 range of six hours. A 2000 presentation authored by
 Nørgaard acknowledged low bioavailability and high vari-
 ation of absorption as known problems with using desmo-
 pressin to treat nocturia, hypothesized that “[t]he need for
 high plasma levels of desmopressin” to achieve an antidiu-
 retic effect “is overestimated,” and suggested that in-
 creased desmopressin doses may pose a safety issue.
 S.A. 4431–32, 4435, 4455. 2 Ferring initiated a follow-on
 study in October 2000, shepherded by Nørgaard and
 Senderovitz, to model the desmopressin dose-response re-
 lationship. The results of the follow-on study supported
 their hypothesis that low doses and plasma concentrations
 of desmopressin could be clinically effective.
     As Fein recalls events, Ronald V. Nardi, a Ferring em-
 ployee, approached him in 2001 seeking assistance with a
 Ferring project involving clinical studies using a desmo-
 pressin oral tablet to treat adult nocturia. Nardi sought
 ideas from Fein regarding how to minimize the high inci-
 dence of hyponatremia Ferring had observed in its clinical
 trials. Hyponatremia is a condition in which sodium levels
 in the blood fall to abnormally low levels, and can lead to
 seizures, cardiac arrhythmias, cerebral edema, and death.
 Fein recounts that, in August 2001, he suggested to Nardi

    2     “S.A.” refers to the corrected supplemental appen-
 dix filed by the parties on September 17, 2020. Corrected
 Supplemental Appendix, Ferring B.V. v. Allergan, Inc.,
 No. 20-1098 (Fed. Cir. Sept. 17, 2020), ECF No. 39.
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 4                               FERRING B.V.   v. ALLERGAN, INC.

 that hyponatremia could be reduced or avoided by using
 lower dosages of desmopressin than Ferring had previously
 tested, and that such dosages could be administered in a
 waterless orodispersible form (a “melt”) sublingually
 through the mucosal membranes of the mouth to improve
 bioavailability of the desmopressin.
     In March 2002, Nørgaard and Senderovitz began de-
 signing additional clinical studies to test a new orodispersi-
 ble form of desmopressin known within Ferring as
 “NEWMIN.” By then, a study comparing NEWMIN to Fer-
 ring’s previously marketed tablet had demonstrated that
 the bioavailability of NEWMIN was approximately double
 that of the previously marketed tablet. NEWMIN’s in-
 creased bioavailability “open[ed] up the possibility of stud-
 ying lower doses of desmopressin than currently
 marketed.” J.A. 3632. By April 2002, Ferring had de-
 signed a clinical study protocol, sponsored by Senderovitz
 and designated CS007. CS007 would investigate the phar-
 macokinetics and antidiuretic effect of orodispersible
 desmopressin tablets containing five low doses of desmo-
 pressin alongside a placebo.
     In May 2002, Ferring filed Great Britain Patent Appli-
 cation No. GB0210397.6 covering various dosage forms of
 an orodispersible desmopressin formulation. Ferring’s ap-
 plication includes a claim directed to “[a] pharmaceutical
 dosage form of desmopressin adapted for sublingual ab-
 sorption.” J.A. 286. The application does not list any in-
 ventors.
      When Ferring experienced delays in production of the
 orodispersible tablets to be used in its CS007 study,
 Nørgaard and Senderovitz planned another clinical study
 to investigate the pharmacokinetic and antidiuretic effects
 of various low desmopressin doses. The study was desig-
 nated CS009 and used an intravenous desmopressin for-
 mulation to approximate the CS007 orodispersible doses.
 Fein did not participate in the design of the CS009 clinical
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 FERRING B.V.   v. ALLERGAN, INC.                            5

 study protocol. In June 2002, Fein was selected to oversee
 United States operations of CS009. As part of that role,
 Fein received via email a copy of Ferring’s CS009 clinical
 study protocol. J.A. 3741. After reviewing the protocol,
 Fein suggested certain changes, including converting the
 original dose levels (expressed in nanograms) to doses on a
 per-weight basis (nanograms per kilogram) to accommo-
 date study participants within a greater weight range.
     In September 2002, Ferring filed Application
 No. PCT/IB02/04036 under the Patent Cooperation Treaty
 (“PCT”), claiming priority from Ferring’s Great Britain ap-
 plication. Ferring’s PCT application lists six inventors, in-
 cluding Senderovitz, Fein, and Nardi. Fein and Nardi were
 included as inventors based on Nardi’s representation that
 they had conceived the sublingual route of administration.
 Two months later, Ferring terminated Fein’s consulting
 agreement.
                                II
     From November 21, 2002 to December 14, 2004, Fein’s
 attorney, William Speranza, corresponded with Ferring re-
 garding Fein’s purportedly inventive contribution of the
 sublingual administration route. We refer to the letters
 and emails exchanged between Ferring and Speranza col-
 lectively as “the Speranza correspondence.”
     A letter from Speranza dated November 21, 2002 as-
 serted that Fein invented material included in Ferring’s
 PCT application, characterizing Fein’s contribution as “a
 sublingual, transmucosal route of delivery which affords a
 number of advantages . . . including enabling the effective
 use of formulations having reduced concentrations of
 desmopressin.” J.A. 531. The letter asserted that Fein had
 no obligation to assign to Ferring any rights in inventions
 Fein conceived while consulting for Ferring. Consequently,
 Fein would have ownership rights in any patents that may
 issue from Ferring’s PCT application. Speranza requested
 that Ferring provide copies of all prosecution documents
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 6                               FERRING B.V.   v. ALLERGAN, INC.

 and any documents filed in subsequent national phase ap-
 plications. Ferring and Speranza then exchanged several
 letters regarding the events underlying Fein’s contribu-
 tion. In January 2003, Speranza sent Ferring another let-
 ter reiterating Fein’s “ownership rights in the invention,
 the pending application therefor and any patents that may
 issue on his invention.” J.A. 534. The letter renewed
 Speranza’s request that Fein “be kept fully apprised” of the
 status of Ferring’s PCT application. Id. Speranza also
 raised the possibility that “it may be necessary for [Fein] to
 take steps independent of Ferring as may be necessary to
 protect his interests.” J.A. 534–35.
     Ferring responded on April 9, 2003, advising Speranza
 that it had “now taken the decision to drop the feature
 ‘adapted for sublingual administration.’” J.A. 537. Consid-
 ering the prior art, Ferring found it “clear . . . that the fea-
 ture does not in this context confer a delimitation i.e.
 novelty.” Id. Accordingly, Ferring relayed that Fein would
 “not be one of the designated inventors in the modified PCT
 application to be filed.” Id.
     Approximately one week later, on April 17, Speranza
 sent an email to Ferring stating that Fein “ha[d] no funda-
 mental problem with” Ferring’s decision to omit “the fea-
 ture of sub-lingual administration invented by Dr. Fein.”
 J.A. 539. Speranza stated that “Fein also is the inventor of
 the associated low dosage possibilities enabled by the sub-
 lingual administration route,” expressed Fein’s under-
 standing that this was not “specifically claimed in the UK
 application,” and noted his “assum[ption] that Ferring is
 not pursuing that subject matter in the planned PCT fil-
 ing.” Id. The email also informed Ferring that “Fein is
 planning to himself proceed with pursuing patent protec-
 tion covering the sub-lingual administration route and the
 associated low dosage possibilities enabled by same which
 he invented, all at his own expense going forward and with
 the understanding that Ferring relinquishes any owner-
 ship claims thereto.” Id. Finally, Speranza notified
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 FERRING B.V.   v. ALLERGAN, INC.                           7

 Ferring that Fein “plans to claim priority to [Ferring’s] UK
 application,” and requested that Ferring provide “the par-
 ticulars of the UK filing.” Id.
     On April 29, 2003, Ferring responded, explaining that
 it would not pursue patent protection for the invention de-
 scribed by Speranza in his April 17 letter, because “[t]he
 low dosage possibilities enabled by the sublingual admin-
 istration route are already available in the public domain.”
 J.A. 542. Ferring noted, however, that it “cannot of course
 say now that Ferring will not make any claim as to owner-
 ship of any other material Dr[.] Fein may include in any
 patent application . . . without seeing the text.” Id. With-
 out “knowing what claims for novelty or inventive steps
 [Fein] ha[d] in mind,” Ferring cautioned that it “cannot be
 sure that [Fein’s forthcoming application] does not cover
 matters to which employees of the Ferring Group have con-
 tributed or regarding which Dr[.] Fein is bound to [Ferring]
 by terms of confidentiality.” Id. Ferring provided Fein
 with the filing date and application number for its Great
 Britain application, but refused to provide Fein with a copy
 of the application, asserting that “Fein has no entitlement
 to the patentable subject matter disclosed therein.” Id.
     On May       6, 2003,       Fein filed Application
 No. PCT/US2003/014463, claiming priority from Ferring’s
 Great Britain application and listing Fein as the sole in-
 ventor. Fein’s application claims low-dose pharmaceutical
 compositions comprising desmopressin and methods of
 treating various conditions with such compositions.
 Though some of Fein’s PCT application claims recite
 desmopressin formulations adapted for various routes of
 administration, none of his PCT application claims are lim-
 ited to desmopressin formulations administered sublin-
 gually.
     The next day, Ferring filed a modified PCT application,
 which was assigned Application No. PCT/IB03/02368. Fer-
 ring’s modified application claims priority from Ferring’s
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 8                              FERRING B.V.   v. ALLERGAN, INC.

 Great Britain application and Ferring’s September 2002
 PCT application and does not list Fein as an inventor or
 contain claims directed to sublingual administration of
 desmopressin. Ferring ultimately obtained U.S. Patent
 Nos. 7,569,429 (“the ’429 patent”) and 7,947,654 (“the ’654
 patent”) claiming priority from its Great Britain applica-
 tion.
     During 2003 and 2004, Fein conducted clinical studies
 related to low-dose desmopressin. Relevant here, in Au-
 gust 2003, Fein initiated a study designated CNF Desmo
 PK200301, titled “A Cross-Over Study Investigating the
 Antidiuretic Effects and Pharmacokinetics of Three Low
 Doses of Desmopressin Administered via Intravenous In-
 fusion for 2 Hours in Over-Hydrated Healthy Non-Smoking
 Male and Female Volunteers.” J.A. 653. Fein’s CNF
 Desmo PK200301 used substantially the same protocol as
 Ferring’s CS009 clinical study. Compare J.A. 3823–26,
 with J.A. 4153–56.
     On November 12, 2003, Fein filed U.S. Patent Applica-
 tion No. 10/706,100 (“the ’100 application”) as a continua-
 tion-in-part of his May 2003 PCT application. Like Fein’s
 PCT application, the ’100 application claims low-dose phar-
 maceutical compositions comprising desmopressin and
 methods of treating various conditions with such composi-
 tions. J.A. 651. None of the ’100 application claims are
 limited to desmopressin formulations administered sublin-
 gually. Id. Fein’s May 2003 PCT application published on
 May 21, 2004. His ’100 application published approxi-
 mately two months later on July 15, and ultimately issued
 on September 21, 2010 as U.S. Patent No. 7,799,761 (“the
 ’761 patent”). The ’761 patent claims recite pharmaceuti-
 cal compositions comprising varying low doses of desmo-
 pressin administered by various routes of delivery. Some
 dependent claims further require that the claimed desmo-
 pressin doses establish a particular desmopressin
 plasma/serum concentration range, or that that a particu-
 lar desmopressin plasma/serum concentration range be
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 FERRING B.V.   v. ALLERGAN, INC.                           9

 maintained for a specified duration. None of the claims re-
 cite pharmaceutical compositions limited to sublingual ad-
 ministration.
     On December 9, 2004, Ferring sent Speranza a letter
 advising Speranza that Ferring was “truly surprised” that
 Fein had proceeded with his May 2003 PCT application,
 which “contain[s] an invention to which we believe he has
 no entitlement and which in particular discloses infor-
 mation confidential and proprietary to Ferring.” J.A. 544.
 Ferring’s letter notified Speranza that it would “take all
 necessary steps to protect its rights and interests but be-
 fore taking formal legal action [Ferring] wish[ed] to give
 [Fein] an opportunity to explain himself.” Id. Ferring fur-
 ther informed Speranza that if it “d[id] not receive a full
 and satisfactory explanation within 14 days of this letter
 [Ferring] will commence formal action.” Id.
      Speranza responded five days later, sending Ferring
 two letters on December 14. The first letter reminded Fer-
 ring that it had acknowledged Fein’s intent to proceed with
 his own patent application. Speranza also posited three
 possible reasons for Ferring’s assertion that Fein had “no
 entitlement” to the invention in his published PCT appli-
 cation. First, and “as would appear” from Ferring’s Decem-
 ber 9 letter, Fein’s PCT “application ‘discloses information
 confidential and proprietary to Ferring.’” J.A. 546. Sec-
 ond, Ferring believes “that this low dosage invention of
 Dr. Fein is simply not patentable because of prior art.” Id.
 Third, “Fein is not the inventor of the claimed low dose in-
 vention and/or . . . Fein cannot assert ownership rights to
 it.” Id. Speranza expressed his opinion that “[o]ur dealings
 and communications throughout 2003 made clear that Fer-
 ring made no claim to low dosage desmopressin as its in-
 vention.” J.A. 546–47. Despite the earlier communications
 regarding claims involving the sublingual route of delivery,
 Speranza made no mention of the use of a sublingual route
 for the delivery of low dosages. To the extent Ferring’s al-
 legation referred to misuse of confidential information,
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 10                             FERRING B.V.   v. ALLERGAN, INC.

 Speranza explained that “[w]hatever Ferring data is set
 forth in Dr. Fein’s subject patent application comes solely
 from the text of the UK priority application filed by Ferring
 in May 2002, naming Dr. Fein as a co-inventor.” J.A. 547.
 In closing, Speranza stated that he “trust[ed] this response
 will put this matter to rest.” Id. “[I]n view of the fact that
 Ferring itself published over a year ago the allegedly ‘con-
 fidential and proprietary’ information to which [Ferring’s]
 letter refers,” Speranza deemed it “irresponsible for Fer-
 ring to level such serious accusations at Dr. Fein and to
 threaten immediate legal action based thereon.” Id.
      Speranza’s second December 14, 2004, letter to Ferring
 focused on Ferring’s allegations of misuse of confidential
 information. It acknowledged Ferring’s “apparent concern
 with the content of Dr. Fein’s published applications” and
 informed Ferring that Fein filed a continuation-in-part
 U.S. patent application (i.e., the ’100 application) “which
 has since published as U.S. Patent Application Publication
 No. 2004/0138098, dated July 15, 2004, also directed to low
 dose desmopressin.” J.A. 550. Speranza’s letter stated
 that a copy of the ’100 application was included as an at-
 tachment, but Ferring disputes that it ever received a copy
 of the ’100 application. Referencing Example 8 and Figures
 1–9 of the ’100 application, Speranza’s letter noted that the
 ’100 application “contains data beyond that included in the
 original Ferring UK application,” which data “did not em-
 anate from Ferring.” J.A. 551. This letter was Speranza’s
 last communication with Ferring before Ferring filed suit
 in April 2012.
     With his patent applications pending, Fein took steps
 to commercialize his invention. In 2006, Fein and Samuel
 Herschkowitz formed Serenity Pharmaceuticals Corpora-
 tion and Serenity Pharmaceuticals, LLC to raise funds to
 cover the prosecution of Fein’s patents and pursue clinical
 development. In late 2006, Fein founded Reprise Biophar-
 maceutics, LLC, a holding company having five members.
 Fein transferred to Reprise his intellectual property rights
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 FERRING B.V.   v. ALLERGAN, INC.                           11

 related to his claimed desmopressin invention. We refer to
 Reprise, Serenity Pharmaceuticals Corporation, and Se-
 renity Pharmaceuticals, LLC collectively as “Serenity.”
     In May 2007, Fein filed U.S. Patent Application
 No. 11/744,615 (“the ’615 application”) as a divisional of the
 ’100 application. The ’615 application published on Novem-
 ber 15, 2007 and matured into U.S. Patent No. 7,405,203
 (“the ’203 patent”) on July 29, 2008. The ’203 patent claims
 recite methods of administering low doses of desmopressin
 by various routes of delivery to establish various desmo-
 pressin plasma/serum concentration ranges. Some claims
 further require that the plasma/serum concentration range
 be maintained for a specified duration. None of the claims
 recite sublingual administration of desmopressin.
      In July 2008, Fein filed U.S. Patent Application
 No. 12/173,074 (“the ’074 application”) as a continuation of
 the ’615 application. The ’074 application published on
 January 1, 2009 and issued as U.S. Patent No. 7,579,321
 (“the ’321 patent”) on August 25, 2009. The independent
 claims of the ’321 patent recite methods of administering
 low doses of desmopressin by various routes of delivery to
 produce an antidiuretic effect or a particular urine osmo-
 lality in a patient. Several claims of the ’321 patent further
 require that the urine osmolality or antidiuretic effect be
 maintained for a specified duration. Again, none of the
 claims recite sublingual administration of desmopressin.
 We refer to the ’203 patent, ’761 patent, and ’321 patent
 collectively as “the Fein patents.”
     By the end of 2008, Fein had conducted Phase I and
 Phase II clinical studies of a low-dose desmopressin in-
 tranasal spray adapted for transmucosal delivery. Fein
 proceeded with Phase III clinical trials in 2009 and 2010.
 On March 31, 2010, Serenity Pharmaceuticals, LLC and
 Reprise entered into agreements with Allergan Sales, LLC,
 Allergan USA, Inc., and Allergan, Inc. (collectively, “Aller-
 gan”) to develop and commercialize a low-dose
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 12                             FERRING B.V.   v. ALLERGAN, INC.

 desmopressin intranasal spray, assigning all of their
 desmopressin intellectual property rights to Allergan. As
 part of the agreements, Reprise and Serenity Pharmaceu-
 ticals, LLC warranted that there was no threat of litigation
 from any third party regarding the Fein patents. Allergan
 made a $43 million up-front payment to acquire the desmo-
 pressin intellectual property rights.
     On October 12, 2010, Ferring’s counsel filed a request
 for reexamination of Fein’s ’203 patent, arguing that the
 prior art rendered the independent claims anticipated or
 obvious. The U.S. Patent and Trademark Office (“USPTO”)
 rejected Ferring’s request for reexamination of the ’203 pa-
 tent on January 19, 2011.
                              III
     On April 5, 2012, Ferring filed a complaint in district
 court asserting New York state law claims and claims for
 correction of inventorship of the Fein patents under
 35 U.S.C. § 256. The matter was assigned to District Judge
 Robert Sweet. The complaint named Allergan, Serenity,
 Fein, and Nardi as defendants (collectively, “Defendants”).
 Ferring alleged that Ferring scientists Nørgaard and
 Senderovitz should be substituted for Fein as the sole in-
 ventors, or at least added as co-inventors, to the Fein pa-
 tents. Ferring filed an amended complaint in August 2013.
 Defendants answered Ferring’s amended complaint. Aller-
 gan filed counterclaims to correct inventorship of Ferring’s
 ’429 and ’654 patents (which issued from Ferring’s modi-
 fied PCT application), claiming that Fein should be named
 as the sole inventor or as a joint inventor on those patents.
      In April 2015, Allergan moved for summary judgment
 that Ferring’s § 256 claims were barred by equitable estop-
 pel, and the non-Allergan defendants joined in Allergan’s
 motion. Several months later, in September 2015, the dis-
 trict court granted Allergan’s motion for summary judg-
 ment and dismissed Ferring’s § 256 claims.
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 FERRING B.V.   v. ALLERGAN, INC.                          13

     In considering Allergan’s summary judgment motion,
 the district court decided as a threshold matter that con-
 duct occurring before the issuance of the Fein patents could
 give rise to equitable estoppel of Ferring’s claims for cor-
 rection of inventorship. The district court then concluded
 that Ferring’s inaction for over seven years following
 Speranza’s December 2004 letters satisfied the misleading
 conduct prong of equitable estoppel. When Ferring was
 faced with Speranza’s reference “to ‘low dosage’ applica-
 tions of desmopressin as Fein’s inventions,” the district
 court reasoned, Ferring’s response “was not that the low-
 dosage invention was Ferring’s intellectual property, but
 that it was not patentable at all, and that Ferring would no
 longer be pursuing claims directed toward it.” Ferring B.V.
 v. Allergan, Inc., 253 F. Supp. 3d 708, 718 (S.D.N.Y. 2015).
 The district court found Ferring’s threat of “immediate le-
 gal action with respect to [Fein’s PCT] application” mis-
 leading, because “Ferring did not disagree or otherwise
 challenge Mr. Speranza’s assertion that low dosage devel-
 opment was Fein’s intellectual property,” despite the fact
 that “Ferring was aware of two Fein patent applications
 that include claims for low desmopressin doses and low
 desmopressin plasma concentration levels.” Id. Therefore,
 the district court concluded, “Ferring’s present application
 to correct inventorship contradicts its earlier position in
 the Speranza correspondence.” Id. The district court also
 concluded that the reliance and prejudice prongs of equita-
 ble estoppel were satisfied.
     In June 2016, the district court denied Ferring’s motion
 for a stay and for certification of judgment to allow Ferring
 to appeal the equitable estoppel summary judgment ruling.
 The non-Allergan defendants subsequently moved to be
 substituted for Allergan as counterclaim plaintiffs, and the
 district court granted that motion on September 14, 2017.
 Following Judge Sweet’s passing, the action was reas-
 signed to District Judge P. Kevin Castel, who refused to
 reconsider Judge Sweet’s earlier rulings and proceeded to
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 14                             FERRING B.V.   v. ALLERGAN, INC.

 address the counterclaims for correction of inventorship of
 Ferring’s ’429 and ’654 patents. Following a bench trial on
 those counterclaims, the district court entered judgment in
 favor of Ferring, refusing to add Fein to Ferring’s ’429 or
 ’654 patents as either the sole or a joint inventor. Final
 judgment in this matter was entered on September 30,
 2019. 3
     Ferring appeals the district court’s September 2015 eq-
 uitable estoppel decision.        Serenity also appealed
 Judge Castel’s September 2019 judgment on its counter-
 claims, and we consolidated Ferring’s appeal with

      3    Ferring points out that, at least as to Fein’s claim
 of co-inventorship of Ferring’s ’429 and ’654 patents,
 Judge Castel found Dr. Fein’s testimony not credible. Fer-
 ring B.V. v. Allergan, Inc., No. 12-cv-2650, 2019 WL
 6183501, at *11 (S.D.N.Y. Sept. 27, 2019). In the form of a
 supplemental letter pursuant to Federal Rule of Appellate
 Procedure 28(j), Ferring also brought to our attention that
 another district court judge, Chief Judge Colleen
 McMahon, also questioned Fein’s credibility regarding his
 involvement with low-dose desmopressin formulations.
 Ferring Pharm. Inc. v. Serenity Pharm., LLC,
 No. 17-cv-09922, 2020 WL 4926458, at *63 (S.D.N.Y.
 Aug. 21, 2020) (concluding, after bench trial in parallel pro-
 ceeding involving the validity of the ’203 and ’321 patents
 under 35 U.S.C. § 102(f), that “[c]ontrary to his absolutely
 incredible testimony, Dr. Fein did not suggest the idea of a
 ‘low dose that is enabled [by sublingual administra-
 tion]’ . . . to Dr. Norgaard and his colleagues at Ferring”
 (second alteration in original) (citation omitted)).
      While Fein has not moved to strike those references
 and the conclusions reached by those judicial officers on
 differently developed records, we must base our judgment
 on what was—and was not—presented to Judge Sweet dur-
 ing the summary judgment proceedings at issue here.
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 FERRING B.V.   v. ALLERGAN, INC.                              15

 Serenity’s appeal. We subsequently granted Serenity’s mo-
 tion to dismiss its appeal, leaving Ferring’s appeal as the
 only pending appeal. We have jurisdiction pursuant to
 28 U.S.C. § 1295(a)(1).
                           DISCUSSION
     On appeal, Ferring argues that the district court erred
 by: considering conduct that preceded the issuance of the
 Fein patents in the equitable estoppel analysis; resolving
 disputed issues of fact in favor of Defendants; and ignoring
 evidence of Defendants’ unclean hands. We address each
 argument in turn.
                                    I
      Our review of a district court’s grant of summary judg-
 ment of equitable estoppel proceeds in two steps. John
 Bean Techs. Corp. v. Morris & Assocs., Inc., 887 F.3d 1322,
 1327 (Fed. Cir. 2018) (citing Scholle Corp. v. Blackhawk
 Molding Co., 133 F.3d 1469, 1471 (Fed. Cir. 1998)). First,
 applying the law of the regional circuit (here, the Second
 Circuit), we review whether there are genuine issues of ma-
 terial fact. See Accenture Global Servs., GmbH v. Guide-
 wire Software, Inc., 728 F.3d 1336, 1340 (Fed. Cir. 2013)
 (citing Teva Pharm. Indus. v. AstraZeneca Pharm. LP,
 661 F.3d 1378, 1381 (Fed. Cir. 2011)); Fed. R. Civ. P. 56(a).
 The Second Circuit reviews a grant of summary judgment
 de novo, construing the evidence in the light most favorable
 to the nonmoving party and drawing all reasonable infer-
 ences in that party’s favor. Kuebel v. Black & Decker Inc.,
 643 F.3d 352, 358 (2d Cir. 2011) (citation omitted). “Sec-
 ond, we review the district court’s application of equitable
 estoppel for abuse of discretion.” John Bean, 887 F.3d
 at 1327 (citing Radio Sys. Corp. v. Lalor, 709 F.3d 1124,
 1130 (Fed. Cir. 2013)).
                                II
     Ferring first argues that “[t]he district court’s applica-
 tion of equitable estoppel to Ferring’s claims for correction
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 16                             FERRING B.V.   v. ALLERGAN, INC.

 of inventorship under 35 U.S.C. § 256 prior to the issuance
 of any patents is contrary to the plain language of the stat-
 ute and this [c]ourt’s precedent.” Appellants’ Br. 28.
 Stated more clearly, Ferring claims that, because its writ-
 ten exchanges with Fein predated the issuance of the Fein
 patents, those exchanges should not have been factored
 into the court’s equitable estoppel analysis, leaving nothing
 else upon which to predicate the judgment on Ferring’s
 claims. During oral argument, however, Ferring conceded
 that our decision in MCV, Inc. v. King-Seeley Thermos Co.,
 870 F.2d 1568, 1572 (Fed. Cir. 1989), stands for the propo-
 sition that a court may consider pre-issuance conduct in as-
 sessing the application of equitable estoppel to § 256
 claims, and that MCV remains good law. Oral Arg. at 1:48–
 3:02, http://oralarguments.cafc.uscourts.gov/default.aspx?
 fl=20-1098_09032020.mp3.
     MCV applied a formulation of equitable estoppel that
 included an element of “unreasonable and inexcusable de-
 lay in filing suit.” 870 F.2d at 1571. This court subse-
 quently overruled that aspect of the formulation in A.C.
 Aukerman Co. v. R.L. Chaides Constr. Co., 960 F.2d 1020,
 1042 (Fed. Cir. 1992) (en banc), abrogated on other grounds
 by SCA Hygiene Prods. Aktiebolag v. First Quality Baby
 Prods., LLC, 137 S. Ct. 954, 959 (2017). See Aukerman,
 960 F.2d at 1042 (“The test set out in Jamesbury [Corp.
 v. Litton Industrial Products, Inc., 839 F.2d 1544 (Fed. Cir.
 1988))] confusingly intertwines the elements of laches and
 equitable estoppel and is expressly overruled. Delay in fil-
 ing suit may be evidence which influences the assessment
 of whether the patentee’s conduct is misleading but it is not
 a requirement of equitable estoppel.”). All other aspects of
 the analysis in MCV, however, were left intact.
      In MCV, we applied to a correction of inventorship
 claim the rule from “infringement situations” that “an as-
 sertion of right followed by silence on the part of the pa-
 tentee may give rise to an estoppel if the patentee’s silence
 is sufficiently misleading.” 870 F.2d at 1572. The putative
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 co-inventor (and founder of MCV) “conferred with [pa-
 tentee Halsey Taylor’s representative] on drafts of the
 claims” and suggested that he be included as a co-inventor
 on Halsey Taylor’s application. Id. at 1569. When Halsey
 Taylor “responded that company policy prohibited the
 naming of non-employees on company patents,” MCV’s
 founder replied that “the exclusive right to market the wa-
 ter coolers was more valuable to MCV than patent rights,
 and that he would ‘help[] in any way [h]e could to facilitate
 the submission of the . . . patent.’” Id. (alterations in orig-
 inal). When things later soured between the parties with
 respect to their marketing agreement, MCV brought a cor-
 rection of inventorship claim. Id. We affirmed the district
 court’s grant of summary judgment that MCV was equita-
 bly estopped from asserting a correction of inventorship
 claim, noting that “MCV not only remained silent about co-
 inventorship after [its founder’s] 1982 discussion with
 [Halsey Taylor], but affirmatively represented to Halsey
 Taylor that it would assist ‘in any way [it] could’ to obtain
 the patent.” Id. at 1572 (third alteration in original). Be-
 cause MCV’s founder “knew Halsey Taylor was seeking a
 patent, and knew what was being claimed,” we reasoned
 that “it was incumbent upon him timely, explicitly and te-
 naciously to apprise Halsey Taylor of his purported inven-
 torship so it could be maturely considered.” Id. at 1573.
      Retreating from the per se rule it initially advanced,
 Ferring then suggested that Radio Systems and John Bean
 support a rule that “when the scope of the issued patents
 [is] different than what was before the parties that led to
 the alleged misleading conduct or inaction then the defense
 of equitable estoppel cannot apply.” Oral Arg. at 2:47–3:45;
 see Radio Sys., 709 F.3d 1124; John Bean, 887 F.3d 1322.
      Radio Systems does not stand for Ferring’s revised
 rule, however. The two patents at issue in Radio Systems
 differed in claim scope, but only the first-issued patent was
 mentioned in a 2005 demand letter accusing Radio Sys-
 tems’s predecessor of infringement. 709 F.3d at 1126,
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 18                             FERRING B.V.   v. ALLERGAN, INC.

 1131. Radio Systems’s predecessor responded that the
 first-issued patent was invalid. Id. at 1126. The second
 patent issued about two and a half years after the 2005 de-
 mand letter. Id. There was no further communication be-
 tween the parties until 2009, when Radio Systems received
 a second demand letter accusing Radio Systems of infring-
 ing both patents. Id. In 2010, Radio Systems filed an ac-
 tion seeking declaratory judgment of noninfringement and
 invalidity of both patents and the patent owner counter-
 claimed for infringement of both patents. Id. at 1126–27.
 The district court held that equitable estoppel barred the
 patent owner’s infringement claims as to both patents
 based on the 2005 demand letter and subsequent silence.
 Id. at 1130. We affirmed the district court’s holding as to
 the first patent, concluding that Radio Systems and its pre-
 decessor were in privity and equitable estoppel applied to
 Radio Systems as a successor-in-interest. Id. at 1131. We
 then reversed the district court’s holding that equitable es-
 toppel applied to bar the patent owner’s infringement
 claims as to the second patent. Id. Because “[t]he first no-
 tice of infringement to Radio Systems regarding the [sec-
 ond] patent” occurred in the 2009 demand letter, there was
 “simply no misleading conduct or silence by [the patent
 owner] to indicate that it did not intend to enforce the [sec-
 ond] patent against Radio Systems.” Id. Differences in
 claim scope did not alone dictate the second of our conclu-
 sions. It was the absence of any communication regarding
 what became the claims in the second patent that was most
 critical to our holding.
     Nor does John Bean stand for a broad rule that equita-
 ble estoppel does not apply whenever there is a difference
 in scope between the issues implicated in discussions giv-
 ing rise to potentially misleading conduct and the patent
 claims at issue in subsequent litigation. In John Bean, the
 reexamined claims that formed the basis of John Bean’s in-
 fringement suit were “heavily amended” or added following
 an ex parte reexamination twelve years after the
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 defendant’s original demand letter (to which John Bean
 never responded) challenging the validity of the asserted
 patent. 887 F.3d at 1324–26. John Bean did not allege any
 infringing activity occurring prior to the issuance of the
 reexamination certificate. Id. at 1326. We concluded that
 “[t]he district court abused its discretion by applying equi-
 table estoppel to bar John Bean’s infringement action with-
 out considering how the ex parte reexamination affected
 the [asserted] patent claims.” Id. at 1329. Under the cir-
 cumstances presented, we reasoned that John Bean nar-
 rowed its claims during reexamination to such an extent
 that the defendant’s invalidity analysis communicated in
 the demand letter would not apply to John Bean’s reissued
 claims. See id. at 1328. We did not announce a blanket
 rule that any change to claim scope between the time of
 communications giving rise to allegedly misleading con-
 duct and the filing of a patent suit would preclude the ap-
 plication of equitable estoppel.
     As “equitable estoppel is not limited to a particular fac-
 tual situation nor subject to resolution by simple or hard
 and fast rules,” Aukerman, 960 F.2d at 1041, we decline to
 adopt a bright-line rule that equitable estoppel cannot ap-
 ply whenever the scope of the issued patent is different
 than what the parties discussed in communications leading
 to the allegedly misleading conduct. Thus, while differ-
 ences in claim scope are relevant to the equitable estoppel
 inquiry, their mere existence does not render pre-issuance
 conduct or communications irrelevant.
     While we reject Ferring’s bright-line rule with respect
 to the relevance of pre-issuance communications, that does
 not mean material differences in the potential patent
 claims discussed pre-issuance and the claims that ulti-
 mately issue need not be considered. And it, importantly,
 does not mean that such differences may not give rise to
 material issues of fact regarding the implications of any pe-
 riod of silence following pre-issuance communications. We
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 20                              FERRING B.V.   v. ALLERGAN, INC.

 turn to that question in the context of Ferring’s second ar-
 gument.
                               III
     Ferring also asserts that, in granting Defendants’ mo-
 tion for summary judgment, the district court improperly
 resolved issues of fact in favor of Defendants. Ferring prin-
 cipally argues that the district court erred in concluding
 that Ferring engaged in misleading conduct because that
 was not the only possible inference from the evidence. On
 this point, we agree with Ferring.
                                A
     In the “most common situation” giving rise to equitable
 estoppel, “the patentee specifically objects to the activities
 currently asserted as infringement in the suit and then
 does not follow up for years.” Id. at 1042. Equitable estop-
 pel has three elements:
      (1) the patentee engages in misleading conduct
      that leads the accused infringer to reasonably infer
      that the patentee does not intend to assert its pa-
      tent against the accused infringer; (2) the accused
      infringer relies on that conduct; and (3) as a result
      of that reliance, the accused infringer would be ma-
      terially prejudiced if the patentee is allowed to pro-
      ceed with its infringement action.
 John Bean, 887 F.3d at 1327 (citing Scholle, 133 F.3d
 at 1471); see also Aukerman, 960 F.2d at 1041 (quoting
 D.B. Dobbs, Handbook on the Law of Remedies § 2.3, at 42
 (1973)). “To justify summary judgment of equitable estop-
 pel, any inference that a patentee made a misleading com-
 munication by omission or acquiescence ‘must be the only
 possible inference from the evidence.’” SCA Hygiene Prods.
 Aktiebolag v. First Quality Baby Prods., LLC, 767 F.3d
 1339, 1350 (Fed. Cir. 2014) (quoting Aukerman, 960 F.2d
 at 1044), vacated in part on other grounds, 137 S. Ct.
 at 967.
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                                B
     We agree with Ferring that the Speranza correspond-
 ence is subject to interpretation and does not support the
 single inference that Ferring, by its statements in the let-
 ters and subsequent silence, acquiesced in Fein’s sole in-
 ventorship of the material in the Fein patents, particularly
 because the claims in those patents are not limited to, and
 do not even mention, the sublingual route of delivery of
 desmopressin. We conclude that the district court erred
 when it concluded as a matter of law that “Ferring’s pre-
 sent application to correct inventorship contradicts its ear-
 lier position in the Speranza correspondence,” Ferring,
 253 F. Supp. 3d at 718, and, accordingly, abused its discre-
 tion in granting summary judgment of equitable estoppel.
                                1
     The district court’s decision rested on the erroneous
 view that the scope of the Speranza correspondence and the
 scope of Fein’s application claims were commensurate with
 the scope of Fein’s issued claims. The district court abused
 its discretion by applying equitable estoppel to bar Fer-
 ring’s § 256 claims because it failed to address material dif-
 ferences in the scope of Fein’s issued patent claims as
 compared to the invention described in the Speranza corre-
 spondence and Fein’s application claims. See John Bean,
 887 F.3d at 1329.
     To be sure, the parties understood from the Speranza
 correspondence that Ferring disavowed any ownership
 claim to the sublingual, transmucosal route of delivery of
 desmopressin and its associated low-dosage possibilities
 that Fein identified as his invention in the Speranza corre-
 spondence. When Fein advised Ferring that he intended
 independently to pursue patent protection for “the sub-lin-
 gual administration route and the associated low dosage
 possibilities enabled by same,” J.A. 539, Ferring responded
 that it “will not be pursuing this claim” because “[t]he low
 dosage possibilities enabled by the sublingual
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 22                              FERRING B.V.   v. ALLERGAN, INC.

 administration route are already available in the public do-
 main,” J.A. 542.
      But, contrary to those representations to Ferring, Fein
 did not pursue patent protection for claims limited to sub-
 lingual (or transmucosal) administration of desmopressin.
 Instead, Fein pursued claims untethered to sublingual ad-
 ministration of desmopressin. E.g., J.A. 587–89. In fact,
 most of Fein’s PCT application claims are untethered to
 any route of administration. Most of Fein’s PCT applica-
 tion claims cover pharmaceutical compositions comprising
 various low doses of desmopressin, some of which are fur-
 ther limited to require that the claimed pharmaceutical
 composition is effective to establish various desmopressin
 plasma/serum concentrations. Indeed, none of Fein’s PCT
 or ’100 application claims and none of his issued claims are
 limited to sublingual administration of desmopressin. See
 ’203 patent at col. 28, ll. 7–56; ’321 patent at col. 28, l. 34–
 col. 30, l. 18; ’761 patent at col. 28, l. 39–col. 30, l. 19;
 J.A. 587–89, 651. Very few of Fein’s PCT or ’100 applica-
 tion claims and very few of his issued claims are limited to
 a transmucosal route of administration. See id. Fein’s PCT
 and ’100 application claims are a sweeping departure from
 his sublingual low-dose desmopressin invention as he de-
 scribed it to Ferring. Importantly, Fein sought patent pro-
 tection for his claims despite Ferring’s prior warning to
 him that Ferring could not “say now that Ferring will not
 make any claim as to ownership of any other material Dr[.]
 Fein may include in any patent application . . . without see-
 ing the text.” J.A. 542. In view of Ferring’s representation
 to Fein that it could not disclaim ownership of any material
 beyond the sublingual administration route and associated
 low-dose possibilities, a reasonable factfinder could con-
 clude that it would have been unreasonable for Fein to in-
 fer from Ferring’s pre-2004 communications that Ferring
 intended to relinquish inventorship rights in the issued
 claims of the Fein patents.
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 FERRING B.V.   v. ALLERGAN, INC.                            23

      Serenity argues that Ferring did acquiesce in Fein’s in-
 ventorship of patent claims untethered to the sublingual
 route of administration when it remained silent after
 learning, in December 2004, “of exactly what [Fein] was
 claiming—through the claims in his published PCT Appli-
 cation and ’100 Application.” 4 Appellees’ Br. 32. The dis-
 trict court agreed with Serenity, resting its decision that
 Ferring engaged in misleading conduct in part on its deter-
 mination that “[t]he low-dosage invention as described in
 the PCT at issue in the Speranza correspondence is the
 same subject matter detailed in the patents-in-suit, down
 to the specific numerical quantity of desmopressin to be
 used.” Ferring, 253 F. Supp. 3d at 718. The district court
 implicitly concluded that Ferring had notice of the inven-
 tion in Fein’s issued claims as of Ferring’s December 2004
 letter, by virtue of that letter’s reference to Fein’s 2003 PCT
 application.

     4    Though Speranza’s second December 14, 2004 let-
 ter states that Speranza included a copy of the ’100 appli-
 cation with the letter, J.A. 550, Ferring argues that no copy
 was ever provided, Reply 24. Regardless, our assessment
 of Fein’s PCT application applies equally to the ’100 appli-
 cation, because like Fein’s PCT application, the ’100 appli-
 cation does not recite any claims with a duration of action
 limitation. See J.A. 651.
      There is no evidence that Ferring had notice of Fein’s
 ’615 application (filed in 2007) or his ’074 application (filed
 in 2008), which matured into Fein’s method of treatment
 patents. Indeed, the Speranza correspondence does not in-
 dicate that Fein was pursuing any additional patents be-
 yond those he expressly identified by application number.
 On this record, a reasonable factfinder could conclude that
 Ferring had no obligation or incentive to monitor patent
 filings to identify any additional patent applications Fein
 had chosen to prosecute.
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 24                                FERRING B.V.   v. ALLERGAN, INC.

     But that conclusion rested on an inadequate claim
 scope analysis, particularly as to Fein’s issued claims con-
 taining duration of action limitations. In discussing the
 relative scope of Fein’s issued claims and the application
 claims, the district court did not point to any claims. In-
 stead, the district court stated only that “[t]he low-dosage
 invention as described in the PCT at issue in the Speranza
 correspondence is the same subject matter detailed in the
 patents-in-suit, down to the specific numerical quantity of
 desmopressin to be used.” Id. The district court’s conclu-
 sion that the claim scope of Fein’s issued claims is the same
 as that of his application claims fails to account for the fact
 that most of Fein’s issued claims contain duration of action
 limitations completely absent from Fein’s application
 claims. Compare, e.g., ’203 patent at col. 28, ll. 7–56, with
 J.A. 587–89. Ferring based its § 256 claims in part on the
 very duration of action limitations the district court over-
 looked. See, e.g., Complaint at 26–33, Ferring B.V. v. Al-
 lergan, Inc., No. 12-cv-2650 (S.D.N.Y. Apr. 5, 2012), ECF
 No. 1; J.A. 1155 (“Indeed, the ’203, ’321, and ’761 patents
 claim the very . . . duration of action (around 4–6 hours)
 that Dr. Norgaard and Dr. Senderovitz developed before
 any of Fein’s alleged conversations with Nardi.”).
     In the absence of notice to Ferring of Fein’s claim to
 inventorship of the duration of action limitations, a reason-
 able factfinder could find that Ferring did not mislead Fein
 regarding Ferring’s claims of inventorship with respect to
 any of Fein’s application claims or issued claims reciting a
 duration of action limitation.
                               2
     Setting aside the differences in scope between Fein’s
 application claims and his issued claims, and the parties’
 dispute as to whether Ferring ever received or reviewed a
 copy of the ’100 application, we must vacate the district
 court’s summary judgment of equitable estoppel because
 the district court’s interpretation of the Speranza
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 correspondence is not the only reasonable one. See SCA
 Hygiene, 767 F.3d at 1350 (“To justify summary judgment
 of equitable estoppel, any inference that a patentee made a
 misleading communication by omission or acquiescence
 ‘must be the only possible inference from the evidence.’”
 (quoting Aukerman, 960 F.2d at 1044)).
      In December 2004, Ferring wrote to Fein expressing
 surprise that Fein had proceeded with his PCT “application
 containing an invention to which [Ferring] believe[s] he
 has no entitlement and which in particular discloses infor-
 mation confidential and proprietary to Ferring to which
 Dr[.] Fein had confidential access during his agreement as
 [a] consultant.” J.A. 544. Ferring’s letter provided an ex-
 ample, noting that Ferring’s confidential results from its
 CS004 study “appear virtually verbatim” on page 30 of
 Fein’s PCT application. Id. Ferring further informed Fein
 that “Ferring will take all necessary steps to protect its
 rights and interests,” and stated that Ferring would “com-
 mence formal action” if it “d[id] not receive a full and satis-
 factory explanation within 14 days.” Id.
     Serenity argues that Ferring’s December 2004 letter
 stated concerns regarding both Fein’s use of Ferring’s con-
 fidential information and Fein’s lack of inventorship inter-
 est (i.e., lack of “entitlement”) in the invention in his
 published PCT application. Though Serenity’s position is
 not unreasonable, Ferring’s December 2004 letter could
 also reasonably refer only to Ferring’s concerns regarding
 Fein’s use of Ferring’s confidential information. A reason-
 able factfinder could interpret Ferring’s use of the phrase
 “and which in particular” to explain further the basis for
 Ferring’s assertion that Fein had “no entitlement” to the
 invention in his PCT application, rather than to state
 Fein’s misuse of confidential information as a separate con-
 cern from lack of “entitlement.”
     Speranza’s December 2004 responses confirm that Fein
 contemporaneously understood Ferring’s “no entitlement”
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 26                             FERRING B.V.   v. ALLERGAN, INC.

 assertion to lend itself to multiple reasonable interpreta-
 tions. Indeed, Speranza’s first responsive letter “con-
 fess[ed] to not entirely understanding” Ferring’s “no
 entitlement” assertion and set forth three alternative in-
 terpretations. J.A. 546. First, and “as would appear” from
 Ferring’s December 2004 letter, Ferring’s “‘no entitlement’
 statement relates to the assertion that the application ‘dis-
 closes information confidential and proprietary to Fer-
 ring.’” Id. Second, Ferring’s “no entitlement” assertion
 could “refer[] to the belief of Ferring that this low dosage
 invention of Dr. Fein simply is not patentable because of
 prior art, as was expressed in [Ferring’s] letter of 29 April
 2003.” Id. Third, Ferring’s “no entitlement” assertion
 could be “somehow intended to suggest that Dr. Fein is not
 the inventor of the claimed low dose invention and/or that
 Dr. Fein cannot assert ownership rights to it.” Id.
      Elaborating on the third possibility, Speranza mischar-
 acterized Ferring’s April 29, 2003 letter as “confirm[ing]
 that Ferring would not be pursuing any claim with respect
 to low dose desmopressin.” J.A. 547. In fact, in that letter,
 Ferring explained only that it would not pursue claims di-
 rected to “[t]he low dosage possibilities enabled by the sub-
 lingual administration route.” J.A. 542 (emphasis added).
 To the extent Speranza’s articulation of the third possibil-
 ity gave rise to a duty for Ferring to respond, a reasonable
 factfinder could find that Speranza’s blatant mischaracter-
 ization of the scope of Ferring’s prior disclaimer relieved
 Ferring of any such duty.
      In finding that Ferring’s December 2004 threat of “im-
 mediate legal action” and subsequent silence misled Fein
 into thinking that Ferring had relinquished any inventor-
 ship rights in the inventions claimed in Fein’s PCT and
 ’100 applications, the district court cast aside Speranza’s
 first two interpretations of Ferring’s “no entitlement” as-
 sertion in favor of the third. See Ferring, 253 F. Supp. 3d
 at 718. As the third possibility bears the closest relation to
 the inventorship dispute underlying Ferring’s subsequent
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 FERRING B.V.   v. ALLERGAN, INC.                            27

 § 256 claims, the district court’s decision to credit the third
 possibility over the first two drew an inference against Fer-
 ring. This was improper at summary judgment, particu-
 larly when the evidence shows that Fein believed the first
 possibility to be the most likely. 5 See Kuebel, 643 F.3d
 at 358 (explaining that at summary judgment, courts are
 to “constru[e] the evidence in the light most favorable to
 the nonmoving party”). In view of the varying reasonable
 interpretations of the Speranza correspondence, we must
 vacate the district court’s summary judgment of equitable
 estoppel and remand for further proceedings. See SCA Hy-
 giene, 767 F.3d at 1350.
                                IV
     Finally, Ferring asserts that the district court erred in
 deciding that Ferring was equitably estopped from assert-
 ing its § 256 claims because the court failed to consider
 “other evidence and facts respecting the equities of the par-
 ties.” Appellants’ Br. 49 (quoting Aukerman, 960 F.2d
 at 1043). Specifically, Ferring maintains that in assessing
 Defendants’ unclean hands, the district court erred by ig-
 noring evidence that Fein intentionally and deliberately
 copied Ferring’s CS009 clinical study protocol for use in his
 own clinical studies. While we have already concluded that
 a remand is appropriate for other reasons, we address this
 issue because it will remain live on remand.
     “[T]he trial court must, even where the three elements
 of equitable estoppel are established, take into considera-
 tion any other evidence and facts respecting the equities of
 the parties in exercising its discretion and deciding
 whether to allow the defense of equitable estoppel to bar
 the suit.” Aukerman, 690 F.2d at 1043. Indeed, “equitable

     5  Having concluded that the district court erred in its
 misleading conduct analysis, we do not address the parties’
 arguments regarding reliance and prejudice.
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 28                             FERRING B.V.   v. ALLERGAN, INC.

 estoppel is not limited to a particular factual situation nor
 subject to resolution by simple or hard and fast rules.” Id.
 at 1041.
     Ferring’s opposition to Defendants’ motion for sum-
 mary judgment of equitable estoppel raised four bases to
 support the argument that Defendants’ unclean hands
 should preclude the district court from granting equitable
 relief. Ferring asserted: (1) Defendants misrepresented
 that Allergan had viewed the Speranza correspondence
 when conducting its diligence review prior to investing in
 Serenity and Reprise; (2) Defendants hired a third party to
 recover confidential Ferring documents from Nardi’s com-
 puter, which documents Ferring had previously deleted
 pursuant to Nardi’s employment agreement; (3) Defend-
 ants’ counsel organized meetings between defense wit-
 nesses to coordinate their testimony, after which Fein
 submitted a supplemental witness statement modifying his
 testimony; and (4) Fein duplicated Ferring’s CS009 clinical
 study protocol in his own CNF Desmo PK200301 clinical
 study, misrepresented it as his own, and subsequently in-
 cluded data from the study in the Fein patents as Exam-
 ple 8. J.A. 1169–71. With respect to Fein’s copying,
 Ferring further argued that Fein had misrepresented to
 the USPTO in his patent applications that he had evalu-
 ated pharmacokinetic parameters at each desmopressin
 dose level. J.A. 1170, 1205–06. Ferring cited evidence that
 Fein did not attempt to measure plasma/serum levels of
 desmopressin in the CNF Desmo PK200301 study before
 he filed his patent applications, because the plasma sam-
 ples from the study were still in frozen storage as of No-
 vember 2006. Id. (citing S.A. 4234).
     Despite the district court’s statement that it “has also
 considered and rejects Ferring’s unclean hands argu-
 ments,” the court discussed only Ferring’s first three argu-
 ments. Ferring, 253 F. Supp. 3d at 721. The district court’s
 opinion does not mention Ferring’s CS009 study or Exam-
 ple 8 of the Fein patents at all. This leaves us no basis to
Case: 20-1098      Document: 40     Page: 29    Filed: 11/10/2020

 FERRING B.V.   v. ALLERGAN, INC.                            29

 infer that the district court considered Ferring’s evidence
 that Fein copied Ferring’s CS009 study and made related
 misrepresentations to the USPTO. We therefore conclude
 that the district court abused its discretion in granting
 summary judgment of equitable estoppel because the court
 failed to consider all relevant evidence regarding the equi-
 ties of the parties. See Aukerman, 690 F.2d at 1043; Roth-
 schild Connected Devices Innovations, LLC v. Guardian
 Protection Servs., Inc., 858 F.3d 1383, 1388 (Fed. Cir. 2017)
 (“A district court abuses its discretion when, as here, it
 ‘fail[s] to conduct an adequate inquiry.’” (alteration in orig-
 inal) (quoting Atl. Research Mktg. Sys., Inc. v. Troy,
 659 F.3d 1345, 1360 (Fed. Cir. 2011))).
                           CONCLUSION
      We have considered the parties’ remaining arguments
 and do not find them persuasive. For the foregoing rea-
 sons, we vacate the district court’s judgment and remand
 for further proceedings consistent with this opinion.
                VACATED AND REMANDED
                              COSTS
     The parties shall bear their own costs.