Court Opinion

ID: 5132198
Source: CourtListenerOpinion
Date Created: 2021-12-07 00:00:56.802754+00
Date Added: 2024-06-11T08:23:28.762579
License: Public Domain

Case: 20-1933    Document: 65    Page: 1   Filed: 11/30/2021

   United States Court of Appeals
       for the Federal Circuit
                  ______________________

   BIOGEN INTERNATIONAL GMBH, BIOGEN MA,
                      INC.,
              Plaintiffs-Appellants

                            v.

         MYLAN PHARMACEUTICALS INC.,
                Defendant-Appellee
              ______________________

                        2020-1933
                  ______________________

    Appeal from the United States District Court for the
 Northern District of West Virginia in No. 1:17-cv-00116-
 IMK-JPM, Judge Irene M. Keeley.
                 ______________________

                Decided: November 30, 2021
                  ______________________

     WILLIAM F. LEE, Wilmer Cutler Pickering Hale and
 Dorr LLP, Boston, MA, argued for plaintiffs-appellants.
 Also represented by ANNALEIGH E. CURTIS, MADELEINE C.
 LAUPHEIMER, LISA JON PIROZZOLO; SCOTT G. GREENE, New
 York, NY; THOMAS SAUNDERS, Washington, DC; PAUL
 WILLIAM BROWNING, J. MICHAEL JAKES, JAMES B. MONROE,
 JASON LEE ROMRELL, Finnegan, Henderson, Farabow, Gar-
 rett & Dunner, LLP, Washington, DC.
Case: 20-1933     Document: 65     Page: 2    Filed: 11/30/2021

 2                            BIOGEN INTERNATIONAL GMBH v.
                                MYLAN PHARMACEUTICALS INC.

    DAVID LEE ANSTAETT, Perkins Coie, LLP, Madison, WI,
 argued for defendant-appellee.   Also represented by
 ANDREW DUFRESNE, EMILY JANE GREB; DAN L. BAGATELL,
 Hanover, NH; SHANNON BLOODWORTH, NATHAN K. KELLEY,
 BRANDON MICHAEL WHITE, Washington, DC; MATTHEW
 GREINERT, Mylan, Canonsburg, PA.
                  ______________________

     Before O’MALLEY, REYNA, and HUGHES, Circuit Judges.
      Opinion for the court filed by Circuit Judge REYNA.
      Dissenting opinion filed by Circuit Judge O’MALLEY.

 REYNA, Circuit Judge.
      This appeal from the United States District Court for
 the Northern District of West Virginia concerns a patent-
 infringement dispute between Biogen International
 GmbH, Biogen MA, Inc., and Mylan Pharmaceuticals, Inc.
 Biogen owns United States Patent 8,399,514 (the ’514 Pa-
 tent), which claims a method of treating multiple sclerosis
 with a drug called dimethyl fumarate. In 2017, Biogen
 filed a lawsuit against Mylan alleging patent infringement.
 Mylan counterclaimed for declaratory judgment that the
 patent was invalid and not infringed. Following a bench
 trial, the district court determined that the asserted claims
 of the ’514 Patent were invalid for lack of written descrip-
 tion. Biogen challenges the district court’s decision on ap-
 peal.
     For the reasons set forth in this opinion, we hold that
 the district court did not clearly err in determining that
 Mylan has established its burden of showing, by clear and
 convincing evidence, that the asserted ’514 Patent claims
 are invalid for lack of written description under 35 U.S.C.
 § 112. Accordingly, we affirm the judgment of the district
 court.
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                         I. BACKGROUND
     Under the Drug Price Competition and Patent Term
 Restoration Act of 1984 (the Hatch-Waxman Act), a manu-
 facturer of a new generic drug that is bioequivalent 1 to a
 previously approved drug may seek approval from the US
 Food and Drug Administration (FDA) to market the ge-
 neric product by filing an Abbreviated New Drug Applica-
 tion (ANDA). See Pub. L. No. 98-417, § 101, 98 Stat. 1585,
 1585–86 (1984) (codified as amended at 21 U.S.C.
 § 355(j)(2)(A)). The statute requires the generic-drug man-
 ufacturer to submit a certification regarding the status of

     1    For purposes of Hatch-Waxman litigation, a ge-
 neric drug is considered bioequivalent to a brand-name
 drug if:
     (i) the rate and extent of absorption of the [generic]
     drug do not show a significant difference from the
     rate and extent of absorption of the listed [brand-
     name] drug when administered at the same molar
     dose of the therapeutic ingredient under similar ex-
     perimental conditions in either a single dose or
     multiple doses; or
     (ii) the extent of absorption of the [generic] drug
     does not show a significant difference from the ex-
     tent of absorption of the listed [brand-name] drug
     when administered at the same molar dose of the
     therapeutic ingredient under similar experimental
     conditions in either a single dose or multiple doses
     and the difference from the listed drug in the rate
     of absorption of the drug is intentional, is reflected
     in its proposed labeling, is not essential to the at-
     tainment of effective body drug concentrations on
     chronic use, and is considered medically insignifi-
     cant for the drug.
 21 U.S.C. § 355(j)(8)(B)(i)–(ii).
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                                 MYLAN PHARMACEUTICALS INC.

 any patent that purportedly protects the brand-name drug,
 including information as to whether no such patent exists
 or the patent already expired, and if the patent has not ex-
 pired the manufacturer must indicate the date on which
 the patent will expire. 21 U.S.C. § 355(j)(2)(A)(vii)(I)–(III).
      If a patent that covers the brand-name drug has not
 expired, the generic-drug manufacturer may file what is
 known as a paragraph IV certification, attesting that the
 “patent is invalid or will not be infringed by the manufac-
 ture, use, or sale of the new drug for which the application
 is submitted.” Id. § 355(j)(2)(A)(vii)(IV). The manufacturer
 filing the ANDA and paragraph IV certification must
 promptly notify the owner of any patent subject to the cer-
 tification. Id. § 355(j)(2)(B)(iii). And the FDA must ap-
 prove the ANDA, unless the patent owner objects by filing
 an action for patent infringement against the generic-drug
 manufacturer within forty-five days of receiving notice of
 the paragraph IV certification. Id. § 355(j)(5)(B)(iii). If the
 patent owner brings the infringement suit under the
 Hatch-Waxman Act within the statutory period, the law
 triggers an automatic, thirty-month stay in the FDA-
 approval process of the generic drug, pending the outcome
 of the litigation. See id. § 355(j)(5)(B)(iii).
     Mylan Pharmaceuticals, Inc. (Mylan) filed an ANDA
 seeking to manufacture, use, and market a generic dime-
 thyl fumarate (DMF) product for the treatment of multiple
 sclerosis (MS) before the expiration date of the ’514 Patent.
 J.A. 6001–02. On June 30, 2017, Biogen International
 GmbH and Biogen MA, Inc. (collectively Biogen) sued
 Mylan for patent infringement in the Northern District of
 West Virginia pursuant to the Hatch-Waxman Act. Id. In
 its original complaint, Biogen asserted six patents2

     2  In addition to the ’514 Patent, Biogen asserted US
 Patents 6,509,376; 7,320,999; 7,619,001; 7,803,840; and
 8,759,393. J.A. 6002.
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 purportedly covering Tecfidera®, Biogen’s trademarked
 DMF-capsule formulation for the treatment of patients suf-
 fering from relapsing-remitting forms of MS. Id. Only the
 ’514 Patent is at issue in this appeal. See J.A. 2–3.
                     A. The ’514 Patent
     The ’514 Patent claims priority to United States Provi-
 sional Application 60/888,921 (the ’921 Application), which
 Biogen filed on February 8, 2007. U.S. Patent No.
 8,399,514, at [60] (filed Feb. 13, 2012) (issued Mar. 19,
 2013). As issued, the patent is entitled “Treatment for
 Multiple Sclerosis.” ’514 Patent, at [54].
      MS is a disabling autoimmune disease that affects the
 central nervous system (CNS) and involves an abnormal
 inflammatory response, which leads to damage and the
 eventual destruction of the myelin sheath that surrounds
 neuronal axons—the nerve fibers that transmit electrical
 signals across CNS nerve cells. See ’514 Patent col. 1
 ll. 15–20. The myelin sheath, which comprises a mixture
 of proteins and lipids, is a substance that acts as a protec-
 tive covering to insulate nerve fibers—much like the insu-
 lation material that surrounds and protects an electrical
 wire—and permits nerve cells to adequately conduct the
 electrical signals. See John S. O’Brien, Stability of the My-
 elin Membrane, 147 SCIENCE 1099, 1099 (1965); J.A. 4–5.
 MS-induced deterioration of the myelin sheath interferes
 with the proper transmission of such electrical signals
 across nerve cells and eventually contributes to neuro-
 degeneration, death of neurons, and progressive neurolog-
 ical dysfunction in individuals suffering from the disease.
 See ’514 Patent col. 1 ll. 17–20, 29–30; J.A. 4–5.
     In its action alleging patent infringement against
 Mylan, Biogen asserted claims 1–4, 6, 8–13, 15, and 16 of
 the ‘514 Patent. J.A. 15–17. Claim 1 is representative and
 recites:
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                                 MYLAN PHARMACEUTICALS INC.

     A method of treating a subject in need of treatment
     for multiple sclerosis comprising orally administer-
     ing to the subject in need thereof a pharmaceutical
     composition consisting essentially of (a) a thera-
     peutically effective amount of dimethyl fumarate,
     monomethyl fumarate, or a combination thereof,
     and (b) one or more pharmaceutically acceptable
     excipients, wherein the therapeutically effective
     amount of dimethyl fumarate, monomethyl
     fumarate, or a combination thereof is about
     480 [milligrams] per day [(mg/day)].
 Id. col. 27 ll. 59–67. Relevant to this appeal is Biogen’s use
 of DMF, a fumaric-acid ester compound, at a specific dose
 of 480 mg/day (DMF480) under the brand name Tecfidera®
 for the treatment of MS.
      The ’514 Patent specification largely tracks that of the
 original ’921 Application, which Biogen entitled “Nrf2
 Screening Assays and Related Methods and Composi-
 tions.” 3 J.A. 3289–92. The specification casts a wide net
 for a myriad of neurological disorders, including neuro-
 degenerative diseases such as amyotrophic lateral sclerosis
 (ALS), Parkinson’s disease, Alzheimer’s disease, and Hun-
 tington’s disease; demyelinating neurological diseases,
 such as various forms of MS and at least twenty-eight other
 disorders related to demyelination; polyneuritis; and mito-
 chondrial disorders with demyelination. See ’514 Patent
 col. 16 ll. 18–63. Although the specification does not focus
 exclusively on MS, it discusses MS-related background

     3   On February 7, 2008, Biogen filed International
 Patent Application PCT/US2008/0016902 (the ’902 Appli-
 cation), which maintained the same title, claims, and in-
 ventor as the ’921 Application but added to its specification.
 J.A. 10. On August 7, 2009, the international ’902 Appli-
 cation entered the national phase and became US Patent
 Application 12/526,296 (the ’296 Application). Id.
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 information in two paragraphs that appear in the first col-
 umn. See id. col. 1 ll. 15–52.
      The specification further describes five methods to ex-
 plore a potential protective role for the activation of the
 Nrf2 pathway in neurodegenerative and neuroinflamma-
 tory diseases. J.A. 66–67. Methods 1–3 relate to screening,
 evaluating, and comparing the bioequivalence of com-
 pounds for their use against neurological diseases.
 J.A. 68–69. Methods 4 and 5 relate to the treatment of such
 neurological diseases. J.A. 69. Consistent with the disclo-
 sure’s original title concerning Nrf2 screening, the totality
 of the specification focuses primarily on drug discovery. In-
 deed, the invention’s title was only amended to “Treatment
 for Multiple Sclerosis” in 2011 after Biogen acquired Phase
 III clinical data for the use of DMF480 in treating MS. See
 J.A. 12–13; J.A. 3490–91.
      Because the claims at issue concern methods to treat
 MS, we must look to methods 4 and 5 as disclosed in the
 specification. Method 5 is largely irrelevant for our pur-
 poses because it relates to combination therapy comprising
 the administration of a compound that upregulates the
 Nrf2 pathway with at least one other compound that can-
 not upregulate the pathway. ’514 Patent col. 8 ll. 54–63.
 But method 4 is instructive, as it discloses “methods of
 treating a neurological disease by administering to the sub-
 ject in need thereof at least one compound that is at least
 partially structurally similar to DMF and/or [monomethyl
 fumarate (MMF)],” as well as “a method of treating a mam-
 mal who has or is at risk for a neurological disease . . . [by]
 administering to the mammal a therapeutically effective
 amount of at least one neuroprotective compound” such as
 DMF or MMF, and “a method of slowing or preventing neu-
 rodegeneration” induced by demyelination or the death or
 neurons. Id. col. 8 ll. 35–53.
     Save for one paragraph in the specification, the disclo-
 sure does not teach potential dosage levels for DMF
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                                MYLAN PHARMACEUTICALS INC.

 monotherapy. The sole DMF-dosage paragraph is not
 linked to treatment of any specific disease but recites:
     Effective doses will also vary, as recognized by
     those skilled in the art, dependent on route of ad-
     ministration, excipient usage, and the possibility of
     co-usage with other therapeutic treatments includ-
     ing use of other therapeutic agents. For example,
     an effective dose of DMF or MM[F] to be adminis-
     tered to a subject orally can be from about 0.1 g to
     1 g per pay, 200 mg to about 800 mg per day (e.g.,
     from about 240 mg to about 720 mg per day; or
     from about 480 mg to about 720 mg per day; or
     about 720 mg per day). For example, the 720 mg
     per day may be administered in separate admin-
     istrations of 2, 3, 4, or 6 equal doses.
 Id. col. 18 ll. 54–64 (emphasis added). As shown above, the
 specification explicitly mentions “effective doses” at vari-
 ous concentration ranges within an overall DMF dosage
 range of 100–1,000 mg/day.
      Importantly for this appeal, the specification reveals
 two crucial aspects of the invention. First, the above para-
 graph features the one and only reference to DMF480 in
 the entire specification, which puts the DMF480 dose that
 the ’514 Patent claims at the bottom end of the spectrum of
 a DMF 480–720 mg/day range. Second, the specification
 defines the term “effective” within a therapeutic, rather
 than drug-discovery, context. Thus, according to the spec-
 ification, the terms “‘therapeutically effective dose’ and
 ‘therapeutically effective amount’ refer to that amount of a
 compound which results in at least one of prevention or de-
 lay of onset or amelioration of symptoms of a neurological
 disorder in a subject or an attainment of a desired biologi-
 cal outcome, such as reduced neurodegeneration (e.g., de-
 myelination, axonal loss, and neuronal death) or reduced
 inflammation of the cells of the CNS.” Id. col. 5 ll. 52–59
 (emphases added).
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     B. Clinical Development and Procedural History
     Between 2004 and 2006, Biogen conducted a Phase II,
 clinical, dose-ranging study to test the efficacy of DMF at
 120, 360, and 720 mg/day concentrations (DMF120,
 DMF360, and DMF720, respectively) for the treatment of
 MS. J.A. 2184–91. The May 2006 results of this study
 showed that DMF720 was efficacious in treating MS, but
 DMF120 and DMF360 were not. J.A. 7. In August 2006,
 the FDA recommended that Biogen add a DMF480 dosing
 regimen in the Phase III study because the lower dose
 “might improve patient compliance and/or minimize drop-
 outs from adverse effects during the study.” J.A. 1724–25.
 According to Biogen, the Phase II lead scientist, Dr.
 O’Neill, had conceived the idea of using DMF480 as early
 as 2003 and advocated testing the DMF480 dose as part of
 the trial in February 2004. J.A. 7. At the time, Biogen had
 decided not to include the DMF480 dose in the study for
 commercial reasons. See J.A. 1364. Although Biogen told
 the FDA that DMF720 was the best option, it eventually
 included DMF480 in the Phase III clinical testing. See
 J.A. 1726. The Phase III results showed efficacy for the
 DMF480 and DMF720 doses. J.A. 2060.
      Based on the 2006 Phase II results—and before start-
 ing the Phase III trial to test the DMF480 dose—Biogen
 filed the provisional ’921 Application on February 8, 2007.
 The original application listed Dr. Lukashev, a Biogen sci-
 entist who, at the time, focused on research related to the
 Nrf2 pathway, as the sole inventor. J.A. 8–10. O’Neill was
 not listed as a co-inventor on the ’921 Application; his name
 was added in 2011 as part of an amendment refocusing the
 invention on methods of treatment for MS, which Biogen
 filed after gathering the Phase III results that demon-
 strated therapeutic efficacy of DMF480. 4 J.A. 3437–39;

     4   Biogen amended the ’296 Application—the na-
 tional-phase application filed in 2009, see supra note 3—
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 J.A. 3481–86. O’Neill, however, had not been involved
 with any of the Nrf2 research that led to the ’514 Patent.
 When asked during trial, Lukashev testified that he did not
 know why O’Neill was added as an inventor. J.A. 1318.
 Lukashev also corroborated the original application’s em-
 phasis on drug discovery by noting that his work had en-
 compassed “a more exploratory nature. It[ was] to explore
 potential for follow-on compound discovery . . . .” J.A. 9 (al-
 teration in original). And, more importantly, he “denied
 that his research could be extrapolated to a clinical dose of
 DMF; it ‘was never the focus of [his] work to inform the
 clinical dosing of [DMF].’” Id. (alterations in original). Be-
 sides the amendments related to inventorship and the in-
 vention’s title, Biogen did not make any other changes to
 the specification. This enabled Biogen to claim a priority
 date of February 8, 2007, despite filing wholly new claims
 alongside the amendments. J.A. 13.
     In 2017, Biogen filed its patent infringement suit
 against Mylan in the Northern District of West Virginia.
 J.A. 6001. Biogen sued after Mylan sought ANDA ap-
 proval to market a generic DMF product for treating MS.
 Mylan counterclaimed for declaratory judgment that the
 ’514 Patent was invalid and not infringed. J.A. 6136–44.

 after acquiring its Phase III clinical-data results in April
 2011. J.A. 10. Biogen left the specification of the ’296 Ap-
 plication unchanged, but it amended the invention’s title
 and claims on June 20, 2011. J.A. 47. On October 28, 2011,
 Biogen subsequently amended the ’296 Application again
 to add O’Neill as an inventor. Id. Biogen then abandoned
 the ’296 Application in favor of US Patent Application
 13/326,426 (the ’426 Application), a continuing application
 filed on February 13, 2012. J.A. 11. The ’426 Application
 eventually led to issuance of the ’514 Patent on March 19,
 2013. Id. Biogen claims a February 8, 2007 priority date
 for the ’514 Patent based on the ’921 Application. Id.
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 The district court held a four-day bench trial starting on
 February 4, 2020. J.A. 1001. On February 5, 2020, the Pa-
 tent Trademark and Appeal Board (Board) issued a final
 written decision in a related inter partes review (IPR) pro-
 ceeding, which Mylan initiated on July 13, 2018 and is the
 subject of a companion case to this appeal. See Mylan
 Pharms. Inc. v. Biogen MA Inc.¸ No. IPR2018-01403,
 2020 WL 582736 (P.T.A.B. Feb. 5, 2020). In the IPR case,
 the Board rejected an obviousness challenge to the asserted
 ’514 Patent claims, which estopped Mylan from litigating
 obviousness issues in the trial court. See J.A. 3 n.2.
     During trial, the parties agreed that, for purposes of
 this case, a person of ordinary skill in the art (POSA) is
 someone with “at least a medical degree, at least three
 years of training in neurology, and at least three years of
 clinical experience treating multiple sclerosis patients.”
 J.A. 20. The parties presented expert testimony from two
 neurologists who treat patients with MS—Dr. Greenberg
 for Mylan and Dr. Wynn for Biogen. J.A. 20. At the con-
 clusion of the trial, the district court found that the speci-
 fication did not reasonably convey to a POSA that the ’514
 Patent inventors had “actually invented” a method of treat-
 ing MS with a therapeutically effective dose of DMF480 as
 of February 8, 2007. J.A. 45. The court also found that
 Biogen’s arguments and Wynn’s testimony that a POSA
 would be drawn to the DMF480 dose upon reading the pa-
 tent specification were “neither credible nor persuasive,”
 J.A. 30–31, and noted that Wynn conceded during cross ex-
 amination that the sole DMF-dosage paragraph in the
 specification did not teach a POSA that DMF480 would be
 therapeutically effective for treating MS, J.A. 31.
      The district court opined that Biogen’s attempt to
 “combin[e] a few selectively[ ]plucked disclosures from the
 specification . . . has been squarely rejected by the Federal
 Circuit.” J.A. 45. Based on the testimony offered at trial,
 the context of the ’514 Patent prosecution history, and “sig-
 nificant omissions from the specification,” the district court
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                                 MYLAN PHARMACEUTICALS INC.

 ultimately concluded that Mylan had satisfied its burden
 of showing by clear and convincing evidence that the as-
 serted ’514 Patent claims were invalid for lack of written
 description under 35 U.S.C. § 112. Id. Biogen now appeals
 the district court’s decision.
                    II. STANDARD OF REVIEW
     Whether a claim meets the written-description require-
 ment is a question of fact, which this court reviews for clear
 error on appeal from a bench trial. Nuvo Pharm. (Ireland)
 Designated Activity Co. v. Dr. Reddy’s Laboratories Inc.,
 923 F.3d 1368, 1376 (Fed. Cir. 2019), cert. denied,
 140 S. Ct. 902 (2020). The clear-error standard requires
 courts to exercise deference when reviewing findings of
 fact, unless there is a “definite and firm conviction that a
 mistake has been made.” Scanner Techs. Corp. v. ICOS
 Vision Sys. Corp. N.V., 528 F.3d 1365, 1374 (Fed.
 Cir. 2008) (internal quotation marks and citation omitted).
 Patent invalidity under the written-description doctrine
 must be established by clear and convincing evidence.
 Hynix Semiconductor Inc. v. Rambus Inc., 645 F.3d 1336,
 1351 (Fed. Cir. 2011). Courts of appeals cannot reweigh a
 district court’s assessment of witness credibility, Advanced
 Magnetic Closures, Inc. v. Rome Fastener Corp., 607 F.3d
 817, 832 (Fed. Cir. 2010), and must take into account the
 “unchallenged superiority” of a district court’s ability to
 make witness-credibility determinations and findings of
 fact, see Salve Regina Coll. v. Russell, 499 U.S. 225, 233
 (1991).
                         III. DISCUSSION
           A. The Written-Description Requirement
     To secure a patent for an invention under the laws of
 the United States, an inventor must comply with the writ-
 ten-description requirement outlined in 35 U.S.C. § 112,
 which prescribes:
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     The [patent] specification shall contain a written
     description of the invention, and of the manner and
     process of making and using it, in such full, clear,
     concise, and exact terms as to enable any person
     skilled in the art to which it pertains, or with which
     it is most nearly connected, to make and use the
     same, and shall set forth the best mode contem-
     plated by the inventor or joint inventor of carrying
     out the invention. 5
 35 U.S.C. § 112 (emphasis added). The statutory mandate
 for a written description as a prerequisite for patenting an
 invention has been a fixture of our laws for more than two
 centuries. The Supreme Court recognized, as far back as
 1822, that the purpose of requiring a written description
 under the Patent Act of 1793 was to “put the public in pos-
 session of what the party claims as his own invention, so
 as to ascertain if he claim[s] anything that is in common
 use, or is already known . . . .” Evans v. Eaton, 20 U.S. 356,
 434 (1822). “[P]ossession as shown in the disclosure,”
 therefore, represents the hallmark of written description.
 Ariad Pharms., Inc. v. Eli Lilly & Co., 598 F.3d 1336, 1351
 (Fed. Cir. 2010) (en banc). The written-description statu-
 tory language has undergone little change despite the en-
 actment and revisions of numerous patent statutes since
 the Founding era. See Univ. of Rochester v. G.D. Searle &
 Co., 358 F.3d 916, 925 (Fed. Cir. 2004).

     5   Following the enactment of the Leahy–Smith
 America Invents Act (AIA), Pub. L. No. 112-29, 125 Stat
 284 (2011), the first paragraph of § 112 was redesignated
 as § 122(a). The AIA amendments, which took effect on
 September 16, 2012, replaced the words “of carrying out his
 invention” in the pre-AIA § 112 with “or joint inventor of
 carrying out the invention” in the current § 112(a).
 125 Stat. at 296–97. The amendments bear no significance
 for purposes of our written-description analysis.
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     This court’s precedents dictate that the § 112 written-
 description “requirement is satisfied only if the inventor
 ‘convey[s] with reasonable clarity to those skilled in the art
 that, as of the filing date sought, he or she was in posses-
 sion of the invention,’ and demonstrate[s] that by disclo-
 sure in the specification of the patent.” Nuvo, 923 F.3d at
 1376–77 (quoting Centocor Ortho Biotech, Inc. v. Abbott La-
 boratories, 636 F.3d 1341, 1348 (Fed. Cir. 2011)). A precise
 definition of the invention is pivotal to establishing posses-
 sion. Amgen Inc. v. Sanofi, 872 F.3d 1367, 1373 (Fed. Cir.
 2017). An applicant may show possession of the claimed
 invention by describing it with all of its limitations using
 “such descriptive means as words, structures, figures, dia-
 grams, formulas, etc.” Lockwood v. Am. Airlines, Inc.,
 107 F.3d 1565, 1572 (Fed. Cir. 1997). The term “posses-
 sion” in the context of written-description jurisprudence
 entails an “objective inquiry into the four corners of the
 specification from the perspective of a [skilled artisan].”
 Ariad, 598 F.3d at 1351.
     Whether a claimed invention satisfies the written-de-
 scription requirement of § 112 will depend on the nature of
 the invention. Enzo Biochem, Inc. v. Gen-Probe Inc.,
 323 F.3d 956, 963 (Fed. Cir. 2002) (citations omitted).
 Thus, the written-description analysis is highly dependent
 on the facts of each case. Nuvo, 923 F.3d at 1383 (citations
 omitted). In general, “written description is judged based
 on the state of the art as of the priority date. . . . [E]vidence
 illuminating the state of the art subsequent to the priority
 date is not relevant to written description.” Amgen, F.3d
 at 1373–74 (internal citation omitted).
             B. Possession of the Claimed Invention
     The core issue in this appeal is whether the specifica-
 tion Biogen filed on February 8, 2007 supports the 2011
 claims that issued in the ’514 Patent. Even more precisely,
 the narrow ground on which this question turns is whether
 the original specification describes “possession” of the
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 claimed therapeutically effective DMF480-dose limitation
 to treat MS.
      The district court began by properly noting that “it is
 the specification itself that must demonstrate possession.”
 J.A. 23 (quoting Ariad, 598 F.3d at 1352). The specifica-
 tion covers a broad array of nearly three dozen neurological
 disorders, and MS may arguably constitute an important
 element of the disclosure from the start. See ’514 Patent
 col. 1 ll. 12–52 (explaining that the overall purpose of the
 invention is to treat “demyelinating neurological diseases,”
 such as MS). Next, DMF appears more than two-dozen
 times throughout the specification, including in the three
 examples listed in the disclosure. The prior art demon-
 strates the existence of a link between DMF-mediated ac-
 tivation of the Nrf2 pathway and the neuroprotective and
 therapeutic effects of said activation, which could be ex-
 ploited for the treatment of certain neurological disorders
 such as MS. See id. col. 5 ll. 20–24. Thus, assuming that
 a skilled artisan would understand the disclosure to be un-
 ambiguously focused on MS despite its inclusion among ap-
 proximately      three-dozen     neurological   disorders—a
 determination we need not reach in this case—the specifi-
 cation may arguably provide adequate information to con-
 vey to a skilled artisan that the invention supports method-
 of-treatment claims directed to MS and, perhaps, that the
 use of DMF may be therapeutically linked to MS treat-
 ment. 6

     6   We note, however, that method 4, which is the only
 relevant method to this appeal, is devoid of any specific ref-
 erence to MS. See ’514 Patent col. 8 ll. 35–53; J.A. 27 (not-
 ing that MS is merely listed as one of a slew of neurological
 diseases). The district court further found that Mylan’s ex-
 pert “credibly testified” that nothing in the specification
 “ties an effective dose of DMF specifically to the treatment
 of MS.” J.A. 29.
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      The skilled artisan would then look in the specification
 for guidance vis-à-vis a suitable therapeutic-DMF dosage.
 This is where the district court noted the lack of written
 description, upon which it primarily based its finding of in-
 validity. The DMF480 dose is listed only once in the entire
 specification. See ’514 Patent col. 18 l. 62. The specifica-
 tion’s sole reference to DMF480 constitutes a significant
 fact that cuts against Biogen’s case, particularly because it
 appears at the end of one range among a series of ranges,
 including DMF concentrations of 100–1,000, 200–800,
 240–720, and 480–720 mg/day. That is in stark contrast to
 DMF720, which is referenced independently as one dose
 and was known to be effective as of the February 2007 pri-
 ority date. The ’514 Patent, as issued, features multiple
 claims that are drawn exclusively to the specific DMF480
 dose, but the specification’s focus on basic research and
 broad DMF-dosage ranges show that the inventors did not
 possess a therapeutically effective DMF480 dose at the
 time of filing in 2007. On this point, Lukashev, the original
 inventor listed in the ’921 Application, offered testimony in
 which he “denied that his research could be extrapolated to
 a clinical dose of DMF; it ‘was never the focus of [his] work
 to inform the clinical dosing of [DMF].’” J.A. 9 (alterations
 in original); see also J.A. 34 (noting that the district court
 found Lukashev’s testimony credible as to the fact that all
 the examples listed in the specification were part of his re-
 search and would not have been “helpful in identifying a
 therapeutically effective” DMF dose). Likewise, the dis-
 trict court credited Mylan’s expert testimony at trial that
 the paragraph containing the sole DMF480 reference fails
 to specifically link an effective dose of DMF to the treat-
 ment of MS. J.A. 29.
     This court has previously held that “[s]atisfaction of
 the description requirement [e]nsures that . . . a claim sub-
 sequent to the filing date of the application was sufficiently
 disclosed at the time of filing so that the prima facie date
 of invention can fairly be held to be the filing date of the
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 application.” Vas-Cath Inc. v. Mahurkar, 935 F.2d 1555,
 1562 (Fed. Cir. 1991) (quoting In re Smith & Hubin,
 481 F.2d 910, 914 (CCPA 1973)). An inventor need not
 “prove that a claimed pharmaceutical compound actually
 achieves a certain result. But when the inventor expressly
 claims that result, our case law provides that [such] result
 must be supported by adequate disclosure in the specifica-
 tion.” Nuvo, 923 F.3d at 1384. Based on the evidence in
 the record, the district court did not clearly err in deter-
 mining that Mylan established its burden of showing, by
 clear and convincing evidence, that the specification does
 not adequately support the asserted claims of the ’514 Pa-
 tent. More specifically, the district court did not clearly err
 in finding that a skilled artisan would not have recognized,
 based on the single passing reference to a DMF480 dose in
 the disclosure, that DMF480 would have been efficacious
 in the treatment of MS, particularly because the specifica-
 tion’s only reference to DMF480 was part of a wide DMF-
 dosage range and not listed as an independent therapeuti-
 cally efficacious dose.
     That Biogen later established the therapeutic efficacy
 of DMF480 is of no import to the written-description anal-
 ysis. What matters for purposes of the inquiry in this case
 is whether, at the time of filing the disclosure—well before
 the Phase III study even commenced—a skilled artisan
 could deduce simply from reading the specification that
 DMF480 would be a therapeutically effective treatment for
 MS. As to this point, the specification’s focus on drug dis-
 covery and basic research further buttresses the district
 court’s conclusion that the specification lacks an adequate
 written description to support the DMF480 claims. At the
 time of filing the original disclosure in 2007, the Nrf2 in-
 sights that proved critical in the Phase III study had not
 yet been translated to clinical use. See J.A. 35 (finding
 that, based on the evidence presented at trial, Lukashev’s
 research related to Nrf2 activation and small-molecule
 screening “had nothing to do with the clinical development
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 of Tecfidera®”). Regardless of whether O’Neill had in fact
 hypothesized or even conceived the idea of treating MS
 with a DMF480 dose as early as 2003, see J.A. 1586–87, the
 law is clear that a patent cannot be awarded for mere the-
 oretical research without more, see Ariad, 598 F.3d
 at 1353. The written-description requirement limits pa-
 tent protection only to individuals who perform the difficult
 work of producing a complete and final invention featuring
 all its claimed limitations and publicly disclose the fruits of
 that effort. Id. We therefore determine that, based on the
 evidence in the record, the district did not clearly err in
 finding that Biogen did not possess an invention directed
 to the specific use of a therapeutically effective DMF480
 dose for the treatment of MS as of 2007.
     Confronted with the lack of a specific reference to
 DMF480, Biogen and its expert argued that a skilled arti-
 san would be drawn to the DMF480 dose because it was
 “anchored” to the effective DMF720 dose. J.A. 1548–49.
 But the very same sentence in the specification that dis-
 closes the DMF 480–720 mg/day range also “anchors”
 DMF240 (a known ineffective dose) to DMF720 (according
 to the DMF 240–720 mg/day range). See ’514 Patent col.
 18 ll. 54–64. Not only does the specification anchor an in-
 effective dose, it also expands the purported range of ther-
 apeutic efficacy from DMF100 and DMF200 (doses that a
 skilled artisan would expect to be ineffective) to DMF1,000
 (a dose well above the therapeutically effective DMF720
 mg/day dose). See id. col. 18 ll. 54–64; Appellee’s Br. 26.
 That column 18 of the ’514 Patent specification recites sev-
 eral DMF doses in the 100–1,000 mg/day range as “effec-
 tive” without even identifying a target disease is further
 indicative that the inventors were not in possession of a
 complete and final invention as of February 2007.
     Lastly, the court noted that Mylan had impeached
 Wynn’s credibility by pointing out his inconsistent state-
 ments and evasiveness when asked, during the district
 court proceedings, why a skilled artisan would be drawn to
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 the purported DMF480 efficacy upon reading the patent
 specification—all while consistently maintaining that a
 skilled artisan would not have reasonably expected
 DMF480 to provide the therapeutic efficacy claimed in the
 patent during the IPR proceeding. J.A. 31–33. After hear-
 ing live testimony from the parties’ experts at trial, the dis-
 trict court found that the Biogen expert’s opinion that a
 skilled artisan would be drawn to a DMF480 dose was “nei-
 ther credible nor persuasive.” JA 30–31. We discern no
 principled reason to disturb the district court’s assessment
 as to the credibility of Biogen’s expert testimony. See Salve
 Regina Coll. v. Russell, 499 U.S. 225, 233 (1991) (describ-
 ing the “unchallenged superiority” of a district court as to
 the assessment of witness credibility and making findings
 of fact); Highmark, Inc. v. Allcare Health Mgmt. Sys., Inc.,
 701 F.3d 1351, 1366 (Fed. Cir. 2012) (Reyna, J., dissenting
 from the denial of the petition for rehearing en banc) (not-
 ing that intervention as to issues of fact finding should be
 limited to instances of clear error, especially given that “an
 appellate court cannot adequately, if at all, assess credibil-
 ity of [expert] testimony because the witness is not before
 [the appellate panel] in person.”).
      Viewing the record before us in its totality, we discern
 no clear error in the district court’s judgment that Mylan
 established its burden of showing, by clear and convincing
 evidence, that the asserted ’514 Patent claims are invalid
 for lack of written description under 35 U.S.C. § 112.
                             * * *
     Biogen raises several ancillary issues in an effort to re-
 verse the district court decision. For example, Biogen
 claims that the district court “misinterpret[ed] this
 [c]ourt’s ‘blaze[-]marks’ jurisprudence; fail[ed] to consider
 the specification as a whole; erroneously appl[ied] judicial
 estoppel; disregard[ed] the specification’s express disclo-
 sure of the claimed dose because it was not described as the
 most preferred; and confus[ed] the written-description
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 20                            BIOGEN INTERNATIONAL GMBH v.
                                 MYLAN PHARMACEUTICALS INC.

 requirement with principles of obviousness and unexpected
 results.” Appellant’s Br. 2. But our conclusion that the
 district court did not clearly err in finding the ’514 Patent
 invalid for lack of written description under § 112 renders
 all these arguments superfluous.
     Notably, the Dissent claims that the district court le-
 gally erred by conflating therapeutic and clinical efficacy.
 See Dissent Op. at 6, 8. However, when viewed through
 the lens of the ’514 Patent, this is not a legal issue, but a
 factual one. The district court, as the finder of fact, did not
 find it necessary or appropriate to distinguish between
 therapeutic effects and clinical efficacy based on the speci-
 fication’s definition of “therapeutically effective dose” and
 the record before it, and such a determination was not
 clearly erroneous.
      Most notably, the specification’s definition of “thera-
 peutically effective dose” indisputably features both clini-
 cal and therapeutic insignia.           For example, the
 specification defines a “therapeutically effective dose” as
 an “amount of a compound” that results in the “prevention
 or delay of onset or amelioration of symptoms of a neuro-
 logical disorder in a subject,” namely, clinical insignia, “or
 an attainment of a desired biological outcome, such as re-
 duced neurodegeneration (e.g., demyelination, axonal loss,
 and neuronal death) or reduced inflammation of the cells
 of the CNS,” which constitute therapeutic insignia.
 ’514 Patent col. 5 ll. 52–59 (emphases added).
     On redirect examination, Biogen’s expert attempted to
 characterize the specification’s definition as solely describ-
 ing therapeutic effects—“demyelination, axonal loss, and
 neuronal death” as well as “fewer [brain] scars”—that once
 could “see on [an] MRI scan, for example.” J.A. 1553–54.
 He distinguished these from clinical endpoints, such as “a
 person hav[ing] less episodes” or “no[ ] progression” of
 symptoms, including “weakness, numbness, loss of bladder
 or bowel control, [sight deterioration], [and] less relapses.”
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 J.A. 1553. But Biogen’s expert did not explain why these
 improved clinical outcomes would not qualify under the
 first half of the specification’s definition, which focuses on
 preventing, delaying the onset of, or ameliorating “symp-
 toms of a neurological disorder” in patients. ’514 Patent
 col. 5 ll. 52–55 (emphasis added).
     Based on the record, including at least the specifica-
 tion’s definition of a “therapeutically effective dose” and the
 witness and expert testimony, the district court did not find
 it necessary to distinguish between therapeutic effects and
 clinical efficacy with respect to its patentability determina-
 tion, instead electing to consider both under the specifica-
 tion’s definition of “therapeutically effective dose.” We
 determine that such a finding was not clearly erroneous.
     Accordingly, we conclude that the district court did not
 clearly err in determining that the original 2007 disclosure,
 which focused exclusively on screening compounds for acti-
 vation of the Nrf2 biological pathway, did not disclose a
 method to administer a therapeutically effective dose of
 DMF480 for the treatment of MS. Nor did the district court
 clearly err in finding that “O’Neill’s hypothesis, that a
 [DMF480 dose] would be efficacious in treating MS,
 evolved from his review” of confidential information, which
 a skilled artisan would not have been privy to in 2007 and
 was never included in the original disclosure. See J.A. 35,
 42, 1586–87.
     Because we hold that the ’514 Patent is invalid under
 the written-description doctrine, we need not reach the
 merits of the parties’ arguments in the companion IPR
 case.
                        IV. CONCLUSION
     For the reasons set forth in this opinion, we affirm the
 district court’s decision that Mylan satisfied its burden of
 showing, by clear and convincing evidence, that the as-
 serted ’514 Patent claims are invalid for lack of written
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 22                          BIOGEN INTERNATIONAL GMBH v.
                               MYLAN PHARMACEUTICALS INC.

 description under 35 U.S.C. § 112. Viewed in its totality,
 the record shows that the inventors were not in possession
 of a method of administering a therapeutically effective
 dose of DMF480 to treat MS on or before the February 8,
 2007 priority date. We have considered the parties’ re-
 maining arguments and find them unavailing or do not
 reach them.

                       AFFIRMED
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    United States Court of Appeals
        for the Federal Circuit
                   ______________________

   BIOGEN INTERNATIONAL GMBH, BIOGEN MA,
                      INC.,
              Plaintiffs-Appellants

                              v.

          MYLAN PHARMACEUTICALS INC.,
                 Defendant-Appellee
               ______________________

                         2020-1933
                   ______________________

    Appeal from the United States District Court for the
 Northern District of West Virginia in No. 1:17-cv-00116-
 IMK-JPM, Judge Irene M. Keeley.
                 ______________________

 O’MALLEY, Circuit Judge, dissenting.
     While I am loath to reverse district court determina-
 tions that rely heavily on credibility findings, I must re-
 spectfully dissent. There is no dispute over whether the
 district court erred in finding that Biogen was judicially es-
 topped from drawing a distinction between clinical and
 therapeutic effects: it did. Mylan calls the error harmless
 and the majority finds it “ancillary” to its analysis. I, on
 the other hand, believe this threshold error impacted the
 district court’s entire written description analysis. I would
 therefore reverse and remand for reconsideration in light
 of a proper understanding of the distinction between the
 two effects and the written descriptions needed for each.
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                                   MYLAN PHARMACEUTICALS INC.

                                 I.
     A. The district court erred in applying judicial estoppel
      As it had tried to do throughout the trial, Biogen ex-
 plained the distinction between clinical efficacy and thera-
 peutic effects in its post-trial briefs before the district court.
 Clinical efficacy involves the type of scientific rigor associ-
 ated with Phase III clinical trials: the investigative
 DMF480 dose must produce superior clinical endpoints to
 the standard of care for MS, Rebif®. See J.A. 8066. Ther-
 apeutic effects, by contrast, “do not require efficacy on clin-
 ical endpoints or superior efficacy to existing drugs.” Id.
 It, instead, “refer[s] to the amount of [DMF480] which re-
 sults in . . . prevention or delay of onset or amelioration of
 symptoms of a neurological disorder” like MS. ’514 patent,
 col. 5, ll. 52–55.
     Based on this distinction, Biogen took issue in its post-
 trial brief with Mylan’s contention that the ’514 patent
 lacked written description support because “a person of or-
 dinary skill in the art would not have a reasonable expec-
 tation that the 480 mg/day [DMF] dose would provide
 statistically significant and clinically meaningful effective-
 ness for treating MS.” J.A. 8064 (citing Mylan’s post-trial
 brief, which quoted Dr. Dawson’s testimony). Biogen
 pointed out that, in addition to mixing up written descrip-
 tion and obviousness inquiries (which I will discuss infra),
 Mylan’s argument erroneously assumed that the claims re-
 quired clinical efficacy when they only covered therapeutic
 effects. J.A. 8063–66.
     In a two-sentence footnote, the district court concluded
 that Biogen was judicially estopped from pointing out the
 distinction between clinical and therapeutic efficacy. Bio-
 gen Int’l GmbH v. Mylan Pharms. Inc., 2020 WL 3317105,
 at *8 n.15 (N.D.W. Va. June 18, 2020). Citing New Hamp-
 shire v. Maine, 532 U.S. 742 (2001), the district court rea-
 soned that Biogen could not “deliberately chang[e]
 positions according to the exigencies of the moment.” Id.
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      I need not detail why the court’s footnote ruling on ju-
 dicial estoppel constituted an abuse of discretion under
 Fourth Circuit law. See Martineau v. Wier, 934 F.3d 385,
 393 (4th Cir. 2019) (setting out a multi-factor test for the
 judicial estoppel inquiry, which the district court wholly
 failed to apply in this case). Biogen’s briefs explain this
 error in detail and neither Mylan nor the majority defends
 the district court’s ruling under that governing law.
     I will, however, provide detail on how the erroneous ju-
 dicial estoppel ruling led the district court to legally err in
 its interpretation of Federal Circuit written description
 precedent. In my view, the district court’s refusal to
 acknowledge the difference between therapeutic and clini-
 cal effects evinces a fundamental misunderstanding of
 what is claimed—and, thus, what requires written descrip-
 tion support—in the ’514 patent.
     The ’514 patent explains that neurodegenerative disor-
 ders like MS are “characterized by inflammation in parts
 of the [central nervous system (CNS)], leading to the loss
 of the myelin sheathing around neuronal axons (demye-
 lination), loss of axons, and the eventual death of neurons,
 oligodendrocytes and glial cells.” ’514 patent, col. 1, ll. 17–
 20. The ’514 patent discusses the promise of treating MS
 using DMF, “a member of a large group of anti-oxidant mol-
 ecules known for their cytoprotective and anti-inflamma-
 tory properties.” ’514 patent, col. 5, ll. 16–18. The ’514
 patent claims a “therapeutically effective amount” of
 DMF480, which the specification defines as
     that amount of a compound which results in at
     least one of prevention or delay of onset or amelio-
     ration of symptoms of a neurological disorder in a
     subject or an attainment of a desired biological out-
     come, such as reduced neurodegeneration (e.g., de-
     myelination, axonal loss, and neuronal death) or
     reduced inflammation of the cells of the CNS.
 ’514 patent, col. 5, ll. 52–59.
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      Notably, the ’514 patent explains that the inventors
 measured DMF’s therapeutic efficacy in terms of its ability
 to enhance the expression levels of Nrf2—a transcription
 factor that activates the expression of genes responsible for
 protecting cells from the neurodegeneration commonly as-
 sociated with MS. See ’514 patent, col. 5, ll. 16–24; see also
 ’514 patent, col. 1, ll. 35–62. Figures 3 and 4 of the ’514
 patent provide in vivo data showing an increase in Nrf2 ex-
 pression following DMF treatment. ’514 patent, Figures 3
 and 4; see also ’514 patent, col. 22, ll. 1–13. And, the ’514
 patent states: “the finding that DMF activates the Nrf2
 pathway . . . offers a rationale for identification of structur-
 ally and/or mechanistically related molecules that would be
 expected to be therapeutically effective for the treatment of
 neurological disorders, such as, e.g., MS.” ’514 patent, col.
 5, ll. 19–24 (emphasis added). Taken together, it is clear
 on the face of the ’514 patent that the claimed “therapeuti-
 cally effective amount” refers to DMF’s ability to mitigate
 MS symptoms vis-à-vis its modulation of Nrf2 expression;
 it has nothing to do with whether DMF480 outperforms the
 standard of care for MS (Rebif®) in a Phase III clinical trial
 setting.
     It is no wonder, then, why Biogen—in response to
 Mylan’s repeated contentions that the ’514 patent fails the
 written description requirement because it lacks Phase III
 clinical efficacy data—sought in its post-trial briefing to re-
 mind the district court that the written description inquiry
 should focus on therapeutic efficacy. 1 Far from deliberately
 changing positions as the district court accused it of, Bio-
 gen was simply attempting to direct the district court’s at-
 tention to the claim language at issue. Judicially estopping
 Biogen from doing so was not just legally erroneous under

     1    To be sure, Mylan continues its erroneous confla-
 tion of therapeutic and clinical efficacy before our court.
 See, e.g., Appellee’s Resp. Br. at 48–49.
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 Fourth Circuit law, it misapplied our written description
 precedents by ignoring the claims at a time when they
 should have been given primacy. Cf. Phillips v. AWH
 Corp., 415 F.3d 1303, 1312 (Fed. Cir. 2005) (en banc) (“It is
 a bedrock principle of patent law that the claims of a patent
 define the invention to which the patentee is entitled the
 right to exclude.”) (citations omitted) (internal quotation
 marks omitted). 2
     As discussed further below, the impact of the district
 court’s errant refusal to acknowledge the difference be-
 tween therapeutic and clinical efficacy is evident through-
 out the rest of the opinion.

     2    The majority’s argument that there is no ascertain-
 able difference between clinical and therapeutic efficacy is
 wrong for several reasons. See Maj. Op. at 20–21. As I
 have detailed above, the ’514 patent makes clear that “ther-
 apeutically effective amount” does not involve comparing
 the claimed DMF480 dosage to the standard of care for MS
 like a clinical trial would. And, neither party ever argued
 this—either to the district court or on appeal. Biogen, in-
 stead, advocated distinguishing the two while Mylan and
 the district court blithely proceeded as though there were
 no difference without ever providing any explanation. To
 make up for this deficiency in the trial record, the majority
 provides its own explanation: “clinical insignia” is somehow
 encompassed by the ’514 patent’s definition of “therapeuti-
 cally effective dose.” Id. (citing ’514 patent, col. 5, ll. 52–
 59). The majority appears to forget our role in this appeal:
 we are a court of review, not the primary factfinder. To the
 extent the majority fashions its own explanation of why
 therapeutic and clinical efficacy are one in the same, it
 crosses that line.
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 6                             BIOGEN INTERNATIONAL GMBH v.
                                 MYLAN PHARMACEUTICALS INC.

  B. The district court’s conflation of therapeutic and clini-
  cal efficacy caused it to erroneously require clinical data,
                rather than therapeutic effects
     The district court’s failure to distinguish therapeutic
 effects and clinical efficacy also led it to conflate concepts
 of obviousness and written description. This conflation, in
 my view, caused the district court to erroneously require a
 showing of clinical data akin to what would be gathered in
 Phase III clinical trials in its written description analysis.
      Somewhat circularly, after acknowledging that clinical
 data demonstrating effectiveness is not required to satisfy
 written description, the district court went on to find that
 the ’514 patent does not demonstrate possession because it
 lacks clinical efficacy data. Biogen, 2020 WL 3317105, at
 *15. To arrive at this conclusion, the district court relied
 on its interpretation of our precedent in Nuvo. According
 to the district court, the patentees in Nuvo could not estab-
 lish possession because a POSA “would not have expected
 [the claimed drug] to be effective, and nothing in the spec-
 ification would teach a [POSA] otherwise.” Id. (quoting
 Nuvo Pharms. (Ireland) Designated Activity Co. v. Dr.
 Reddy’s Lab’ys Inc., 923 F.3d 1368, 1377, 1381 (Fed. Cir.
 2019) (alteration in original). The district court reasoned
 that the same set of facts are at issue in this case: because
 Biogen had defended against Mylan’s obviousness chal-
 lenges in this case and a related inter partes review pro-
 ceeding by contending that a POSA would not have
 expected the DMF480 dose to clinically treat MS, the ’514
 patent’s failure to teach a POSA otherwise with clinical
 data dooms Biogen’s written description arguments. Id.
 (citing Nuvo, 923 F.3d at 1381).
     This cannot be right. Whether a claim satisfies the
 written description requirement of § 112 is a question of
 fact that we review for clear error. Ariad Pharms. v. Eli
 Lilly and Co., 598 F.3d 1336, 1351 (Fed. Cir. 2010). We
 provide de novo review, however, of a district court’s
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 MYLAN PHARMACEUTICALS INC.

 interpretation of Federal Circuit precedent. Amgen Inc. v.
 Hoechst Marion Roussel, Inc., 314 F.3d 1313, 1337 (Fed.
 Cir. 2003). Our court has long held that “the hallmark of
 written description is disclosure,” meaning that a patent
 must “reasonably convey[] to those skilled in the art that
 the inventor had possession of the claimed subject matter
 as of the filing date.” Ariad, 598 F.3d at 1351.
      Here, the district court’s reading of Nuvo does not ac-
 curately describe what we actually held in that case. The
 patent at issue in Nuvo claimed an acid inhibitor that was
 uncoated and effective at raising pH levels. Nuvo, 923 F.3d
 at 1373–1374, 1378. The patent specification in Nuvo,
 however, specifically discussed a known problem in the
 prior art involving uncoated acid inhibitors’ ineffectiveness
 at raising pH levels. See id. at 1375 (reversing the district
 court for “not explain[ing] why the mere disclosure of [un-
 coated acid inhibitors], coupled with the known disad-
 vantages of coated [acid inhibitors], is relevant to the
 therapeutic effectiveness of uncoated [acid inhibitors],
 which the patent recognized as problematic for efficacy due
 to its potential for destruction by stomach acid”) (emphasis
 added). Since the patentees in Nuvo did nothing to explain
 how the invention purported to overcome the commonly
 known problem with uncoated formulations that the patent
 specification explicitly discussed, our court invalidated the
 patent for lack of written description. Id. at 1381. No-
 where in Nuvo did we overlay a POSA’s reasonable expec-
 tation of success from the obviousness context onto the
 written description inquiry. To the extent Nuvo mentioned
 a POSA’s expectations, it cabined this discussion to what a
 POSA would have expected based on the explicit teachings
 of the patent specification—not of the prior art. See id. at
 1381 (“In light of the fact that the specification provides
 nothing more than the mere claim that uncoated [acid in-
 hibitors] might work, even though persons of ordinary skill
 in the art would not have thought it would work, the spec-
 ification is fatally flawed.”).
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 8                             BIOGEN INTERNATIONAL GMBH v.
                                 MYLAN PHARMACEUTICALS INC.

     The district court’s reliance on Nuvo to conclude that
 Mylan could use Biogen’s own obviousness defenses
 against it in the written description context is, therefore,
 legally erroneous. What a POSA would expect regarding
 clinical efficacy based on the prior art is a distinct question
 from whether a POSA would understand that the inventor
 possessed the claimed invention—i.e., a therapeutically ef-
 fective dose—based on the patent’s written description.
 Since the district court never engaged in a proper written
 description inquiry, I would reverse and remand for further
 proceedings consistent with a proper written description
 analysis that minds the gaps between obviousness and
 written description, as well as therapeutic and clinical effi-
 cacy. 3
  C. The district court’s conflation of therapeutic and clini-
    cal efficacy caused it to erroneously apply our “blaze
                      marks” precedent
      The majority relieves me of the need to discuss the dis-
 trict court’s erroneous conclusion that the ’514 patent does
 not contain enough “blaze marks” to direct a POSA toward
 MS treatment. See Biogen, 2020 WL 3317105, at *10
 (“Method 4 broadly describes treating neurological dis-
 eases with a therapeutically effective amount of DMF; MS
 is merely one such disease ‘among a slew of competing pos-
 sibilities.’”) (citing Novozymes A/S v. DuPont Nutrition Bi-
 osciences APS, 723 F.3d 1336, 1349 (Fed. Cir. 2013)). The
 majority opinion—appearing to recognize this obvious

     3    To the extent the majority accuses the dissent of
 reweighing the district court’s credibility determinations, I
 disagree. See Maj. Op. at 19–20. Because I believe the dis-
 trict court’s misguided interpretation of Nuvo led it to er-
 roneously require clinical efficacy data for the written
 description inquiry, any expert witness testimony on which
 the district court relied to bolster that requirement is also
 legally unsound.
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 error—says it operates under the assumption that the ’514
 patent satisfies written description in this regard. Maj. Op.
 at 15–16. Given the specification’s repeated references to
 MS, that is a wise decision on the majority’s part.
     I do, however, need to discuss the district court’s find-
 ing (an erroneous one, in my view) that the ’514 patent does
 not contain enough “blaze marks” to “‘link’ a therapeuti-
 cally effective amount of DMF to a dose of 480mg/day.” Bi-
 ogen, 2020 WL 3317105, at *10. The district court cites our
 precedent in Ariad, as well as Dr. Greenberg’s trial testi-
 mony, to justify its application of our “blaze marks” prece-
 dent to this case. Id. I do not believe our case law required
 these patentees to include “blaze marks” in the ’514 patent,
 however. And, the district court’s reliance on Dr. Green-
 berg’s testimony to conclude that the patentees should
 have included “blaze marks” only perpetuated its legally
 erroneous interpretation of our case law. See J.A. 1447–49.
      It is axiomatic that, to satisfy the written description
 requirement, a patent specification must “clearly allow per-
 sons of ordinary skill in the art to recognize that [the in-
 ventor] invented what is claimed.” Ariad, 598 F.3d at 1351
 (citations omitted) (alteration in original). This fundamen-
 tal concept gets tested, however, whenever a patent’s spec-
 ification discloses a broad genus and claims a particular
 species contained within that genus. In cases such as
 these, our court has crafted a subgenre within our written
 description jurisprudence that requires patents containing
 laundry list-type disclosures “to provide sufficient ‘blaze
 marks’ to guide a reader through the forest of disclosed pos-
 sibilities toward the claimed compound.” Novozymes, 723
 F.3d at 1346; see also In re Ruschig, 379 F.2d 990, 994–995
 (C.C.P.A. 1967) (“It is an old custom in the woods to mark
 trails by making blaze marks on the trees. It is no help in
 finding a trail or in finding one’s way through the woods
 where the trails have disappeared . . . to be confronted
 simply by a large number of unmarked trees.”). Notably,
 our “blaze marks” jurisprudence does not apply in every
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 10                              BIOGEN INTERNATIONAL GMBH v.
                                   MYLAN PHARMACEUTICALS INC.

 case concerning written description; it, instead, provides a
 useful framework to analyze whether written description
 has been met in cases involving patents containing laundry
 list disclosures. See, e.g., Fujikawa v. Wattanasin, 93 F.3d
 1559, 1571 (Fed. Cir. 1996) (“In the absence of such
 blazemarks, simply describing a large genus of compounds
 is not sufficient to satisfy the written description require-
 ment as to particular species or sub-genuses.”).
      On my reading of the ’514 patent, the district court
 erred as a matter of law by requiring Column 18 to contain
 sufficient “blaze marks” regarding the claimed DMF480
 therapeutically effective dose. Method 4 of the ’514 patent
 provides a general discussion of treating neurological dis-
 eases, such as MS, with therapeutically effective amounts
 of DMF compounds. See ’514 patent, col. 8, ll. 35–53. Col-
 umn 18 picks up where Method 4 left off by indicating
 which specific DMF doses the patentees considered thera-
 peutically effective. See id., col. 18, ll. 52–64. Column 18
 does this by providing ranges of DMF doses—some large,
 see id. at col. 18, ll. 58–60 (“0.1 g to 1 g per [d]ay”), and some
 small, see id., col. 18, l. 61 (“240 mg to about 720 mg per
 day”). Notably, Column 18 contains an express disclosure
 of the claimed DMF480 dose 4; this reference also comes in

      4  The majority’s decision affirming the district court
 partially rests on the fact that the ’514 patent only men-
 tions the claimed DMF480 dose once. Maj. Op. at 16. But
 the majority cites no case law (and I know of none) for the
 proposition that the written description requirement de-
 mands that a patentee recite a claim element repeatedly to
 pass written description muster. The majority does not,
 and cannot, deny that the claimed DMF480 dose is ex-
 pressly disclosed. To the extent the majority’s opinion may
 be read to establish a requirement that a claim element
 must be disclosed multiple times, I dissent from that hold-
 ing as well.
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 the form of a range. See id. at col. 18, l. 62 (“480 mg to
 about 720 mg per day.”).
     I do not believe our “blaze marks” precedent applies to
 the claimed DMF480 dose because Column 18 does not pro-
 vide a laundry list disclosure of therapeutically effective
 doses. Despite providing a varying degree of ranges, Col-
 umn 18 begins one such range with the exact DMF480 dose
 that is claimed. See id. Had the patentees instead listed
 this range as, e.g., “100 mg to about 720 mg per day” and
 expected a POSA to figure out that a 480 mg per day dose
 was therapeutically effective, I would agree that “blaze
 marks” would be necessary to “single out particular trees.”
 In re Ruschig, 379 F.2d at 995. But, because the range pro-
 vided in Column 18 particularly points out the claimed
 DMF480 dose, I believe the claim satisfies Section 112 and
 our corresponding written description jurisprudence. The
 district court’s application of our “blaze marks” precedent
 and corresponding reliance on Dr. Greenberg’s testimony
 thus are erroneous as a matter of law for two reasons.
 First, as discussed above, our “blaze marks” precedent is
 not applicable to this case because Column 18 lacks a laun-
 dry list disclosure. And, second, even if this precedent were
 to apply here, Column 18 provides a sufficient “blaze mark”
 by explicitly mentioning the claimed DMF480 dose. How
 much brighter need a disclosure blaze?
      The district court’s inability to “link” method 4 and Col-
 umn 18, moreover, emanates from its original sin of judi-
 cially estopping Biogen from distinguishing between
 therapeutic and clinical effects. With a proper understand-
 ing of this distinction, the written description analysis in
 this case is straightforward: method 4 provides a general
 description of treating MS using a therapeutically effective
 DMF dose and column 18 demonstrates the patentees’ pos-
 session of the claimed DMF480 dose for that purpose.
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 12                           BIOGEN INTERNATIONAL GMBH v.
                                MYLAN PHARMACEUTICALS INC.

                             II.
      Because I believe the entire course of the district
 court’s analysis might well change if the court were to ad-
 just the lens through which it considers the evidence and
 testimony, I would remand for reconsideration of the record
 with the understanding that the patent is not about clinical
 efficacy—it is about therapeutic effect—and that the writ-
 ten description and obviousness inquiries are not the same.