Seagen Inc. v. Daiichi Sankyo Company, Ltd., Astrazeneca Pharmaceuticals Lp, Astrazeneca Uk Ltd.

United States Court of Appeals
for the Federal Circuit
______________________
SEAGEN INC.,
Plaintiff-Appellee
v.
DAIICHI SANKYO COMPANY, LTD.,
ASTRAZENECA PHARMACEUTICALS LP,
ASTRAZENECA UK LTD.,
Defendants-Appellants
______________________
2023-2424, 2024-1176
______________________
Appeals from the United States District Court for the
Eastern District of Texas in No. 2:20-cv-00337-JRG, Judge
J. Rodney Gilstrap.
______________________
Decided: December 2, 2025
______________________
S ARA T ONNIES HORTON, Willkie Farr & Gallagher LLP,
Chicago, IL, argued for plaintiff-appellee. Also represented
by D EVON WESLEY EDWARDS , New York, NY; D ANE
SOWERS , Washington, DC; MATTHEW A. CHIVVIS , MATTHEW
I AN K REEGER , Morrison & Foerster LLP, San Francisco,
CA; SETH W. L LOYD, BRIAN R OBERT M ATSUI, Washington,
DC; BRYAN J. WILSON, Palo Alto, CA.
CHRISTOPHER N EIL SIPES , Covington & Burling LLP,
Washington, DC, argued for defendants-appellants. Also
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SEAGEN INC. v. DAIICHI SANKYO COMPANY , LTD. 2
represented by BRADLEY K EITH E RVIN, N ICHOLAS L ANE
EVOY , ROBERT J ASON F OWLER.
______________________
Before L OURIE, REYNA , and CHEN, Circuit Judges.
L OURIE, Circuit Judge.
A jury in the United States District Court for the East-
ern District of Texas found that claims 1–5, 9, and 10 of
Seagen Inc.’s (“Seagen”) U.S. Patent 10,808,039 (“the ’039
patent”) were not invalid for lack of written description or
enablement. J.A. 57. The jury further found that Daichii
Sankyo Company, Ltd. AstraZeneca Pharmaceuticals LP,
and AstraZeneca UK Ltd., (collectively, “Daichii”) willfully
infringed at least one of the claims, and awarded Seagen
damages exceeding $41 million. J.A. 56, 58–59. The dis-
trict court denied Daichii’s post-trial motion for judgment
as a matter of law (“JMOL”) and entered final judgment in
favor of Seagen. J.A. 32–52. Because we conclude that the
district court erred in failing to grant JMOL for lack of
written description and enablement, we reverse.
BACKGROUND
I
This case concerns a type of cancer treatment known
as an antibody-drug conjugate (“ADC”). An ADC generally
consists of three components: (1) an antibody, (2) a cyto-
toxic (cell-killing) drug, and (3) a “linker” protein, which
connects the antibody and drug. J.A. 3689 (depicting a sim-
plified ADC). A linker may include different subcompo-
nents. See J.A. 3548. Most relevant to this appeal is one
potential subcomponent called a “peptide unit,” which is
made of a chain of amino acids. See J.A. 3107 (215:2–4).
Peptide units that include two amino acids are called di-
peptides, those with three amino acids are called tripep-
tides, etc. J.A. 3144 (31:20–32:8). Another subcomponent
that may be included in a linker protein is a “spacer unit,”
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SEAGEN INC. v. DAIICHI SANKYO COMPANY , LTD. 3
which is the part of the linker that is directly connected to
the drug moiety (the moiety is the active ingredient within
the drug compound), when present. See J.A. 3548.
Unlike traditional chemotherapies, which are rela-
tively non-selective with respect to the cells they kill, by
combining the cell-targeting abilities of antibodies with the
cell-killing abilities of cytotoxic drugs, an ADC is designed
to kill only cancer cells while sparing healthy cells. J.A.
3139–40 (11:16–13:3). One way in which an ADC functions
is through a mechanism called “intracellular cleavage.” In
principle, when an ADC administered to a patient is de-
signed to intracellularly cleave, the antibody recognizes
and targets specific cells, bringing along with it the linker
and drug moiety. J.A. 3139 (12:17–23). Then, once the
ADC reaches the target cell, it is absorbed into the cell, and
the linker is cleaved (severed) from the antibody, releasing
the drug moiety that kills the target cancer cell. J.A. 3141
(18:2–19:22).
Whether and how a drug moiety is cleaved from the
ADC is determined, in part, by the components of the
linker protein. J.A. 3140 (13:20–14:13). Improper release
of the drug moiety can have deleterious effects. If, for ex-
ample, the ADC releases the moiety before reaching the
target cell, or instead does not release the moiety once in-
ternalized, then the target cell may not receive the optimal
dose, and healthy cells may be exposed to the toxic drug.
J.A. 3106 (209:25–210:17).
Claim 1, the sole independent claim of the ’039 patent,
which is representative, reads as follows:
An antibody-drug conjugate having the formula:
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SEAGEN INC. v. DAIICHI SANKYO COMPANY , LTD. 4
or a pharmaceutically acceptable salt thereof,
wherein:
Ab is an antibody,
S is sulfur,
each —W w— unit is a tetrapeptide; wherein
each —W— unit is independently an Amino
Acid unit having the formula denoted below
in the square bracket:
wherein R19 is hydrogen or benzyl,
Y is a Spacer unit,
y is 0, 1 or 2,
D is a drug moiety, and
p ranges from 1 to about 20,
wherein the S is a sulfur atom on a cysteine residue
of the antibody, and
wherein the drug moiety is intracellularly cleaved
in a patient from the antibody of the antibody-drug
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SEAGEN INC. v. DAIICHI SANKYO COMPANY , LTD. 5
conjugate or an intracellular metabolite of the an-
tibody-drug conjugate.
’039 patent col. 331 l. 36–col. 332 l. 40 (emphases added).
The “Ww” and “Y” limitations of the ’039 patent corre-
spond to the peptide and spacer units that can be included
in the linker protein. J.A. 3147–48 (44:22–45:1). The lim-
itation reciting, “each —Ww— unit is a tetrapeptide,” re-
quires that the claimed peptide unit is a Gly/Phe-only
tetrapeptide. Each of the four —W— units must be the
amino acid depicted in the formula recited in the square
bracket, wherein “R19 is hydrogen or benzyl.” When R19 is
hydrogen, the —W— unit is glycine (abbreviated “Gly” or
“G”), and when R19 is benzyl, the —W— unit is phenylala-
nine (abbreviated “Phe” or “F”). J.A. 3148 (45:8–21). Ac-
cordingly, the Ww unit must be a four-amino-acid-long unit
in which each amino acid is either glycine or phenylala-
nine—i.e., “a Gly/Phe-only tetrapeptide.” J.A. 3148 (45:8–
24). Because phenylalanine can exist in either of two dif-
ferent stereoisomers (spatial arrangements) in addition to
glycine’s one, there are three different options for each
amino acid of the claimed Gly/Phe-only tetrapeptide.
Therefore, the subgenus of peptide units claimed in the
’039 patent encompasses 81 (i.e., 3 4) different species. See
J.A. 3119 (264:21–24). The “Y is a Spacer unit” limitation
does not require any specific amino acid sequence, and is
not at issue in this appeal. ’039 patent col. 331 l. 63.
The ’039 patent, which was filed in July 2019, is a con-
tinuing application of U.S. Application 10/983,340, filed in
November 2004 (“the 2004 application”), from which it
claims priority. ’039 patent, Related U.S. Application
Data; see J.A. 5628–5895. The 2004 application describes
an ADC with the same general formula as the ’039 patent—
i.e., an antibody, a drug moiety, and a linker protein with
a peptide unit (“Ww”) that connects the two, J.A. 5711–14,
but the 2004 application does not explicitly disclose a
Gly/Phe-only tetrapeptide. That was the particular
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SEAGEN INC. v. DAIICHI SANKYO COMPANY , LTD. 6
difference between the claims of the ’039 patent and the
2004 application. The 2004 application only discloses that
the linker protein may contain a peptide unit which is a
tetrapeptide, and that glycine and phenylalanine are pos-
sible amino acid options for the peptide unit. J.A. 5722–23.
The 2004 application does disclose an exemplary tetrapep-
tide with the formula: glycine, phenylalanine, leucine (ab-
breviated “Leu” or “L”), glycine (“GFLG”). J.A. 5727; see
J.A. 5724 (Table IX: “H,” “benzyl,” “isobutyl,” and “H”), J.A.
3148 (48:8–21 (the amino acid with isobutyl is leucine)),
but, again, no disclosure of a tetrapeptide containing only
glycine and phenylalanine. The 2004 application’s descrip-
tion of specific ADCs is also limited to the class of drugs
known as dolastatin/auristatin derivatives (“D/A-type
drugs”). J.A. 5642.
In November 2011, Daichii invented DS-8201, an ADC
marketed under the brand name Enhertu®, used to treat
various types of cancer. J.A. 3113 (240:20–21), 3196
(239:11–16), 3198 (248:7–8). Enhertu contains an amino
acid unit with the sequence: Gly-Gly-Phe-Gly, a Gly/Phe-
only tetrapeptide. J.A. 3196 (240:22–241:7). Enhertu’s
structure and mechanism of action were made publicly
known in December 2015. J.A. 3242 (126:8-10). One can-
not avoid the suspicion that the ’039 patent was filed spe-
cifically to encompass Enhertu, which of course is
permissible if it was entitled to a filing date antedating any
public disclosure of Enhertu. That is the primary issue in
this case.
II
In October 2020, shortly after the ’039 patent was
granted, Seagen filed suit against Daichii in the Eastern
District of Texas, asserting infringement of claims 1–5, 9,
and 10 of the ’039 patent. J.A. 10846–58. AstraZeneca, a
later collaborator on Enhertu, subsequently intervened in
the litigation, joining Daichii as a codefendant. J.A.
10859–61. In parallel with the district court proceedings,
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SEAGEN INC. v. DAIICHI SANKYO COMPANY , LTD. 7
in December 2020, Daichii and AstraZeneca petitioned for
post-grant review (“PGR”) of the asserted claims, which the
United States Patent Trial and Appeal Board (“the Board”)
granted. Daiichi Sankyo, Inc. v. Seagen Inc., No.
PGR2021-00030 (P.T.A.B. Feb. 14, 2023), Paper 36 (insti-
tution decision).
At claim construction before the district court, the par-
ties disputed the meaning of the term “D is a drug moiety”
as used in claim 1 of the ’039 patent. J.A. 1286–87. Daichii
contended that the term should be confined to D/A-type
drugs, but the district court rejected that argument. J.A.
at 1286. The district court reasoned that because neither
the text of the claim nor the specification requires the drug
used in the ADC to be a particular type of drug, “D is a drug
moiety” should be given its plain meaning, encompassing
any drug moiety. J.A. at 1287–92.
At trial, the parties disputed both validity and infringe-
ment. The issues, in part,1 converged on whether the 2004
application provided written description support for a
Gly/Phe-only tetrapeptide, the Ww peptide unit recited in
claim 1, thus entitling the ’039 patent to the 2004 applica-
tion’s November 2004 priority date. Because the jury had
found that Enhertu meets each limitation of one of the as-
serted claims, the priority date of the ’039 patent became
critical: If the 2004 application provided adequate written
description support for its claims, Enhertu would infringe
a valid ’039 patent. But if the 2004 application did not pro-
vide adequate written description support for its claims,
the public disclosure of Enhertu would anticipate them,
and thus invalidate, with, accordingly, no infringement.
1 Daichii presented separate arguments as to why
Enhertu did not infringe the ’039 patent, but those argu-
ments are not at issue in this appeal.
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SEAGEN INC. v. DAIICHI SANKYO COMPANY , LTD. 8
2004 Application
Filed
Enhertu Publicly
Disclosed
039 Application
Filed
Seagen Files Suit
Against Daichii
Nov. 2004 Dec. 2015 July 2019 Oct. 2020
The below timeline illustrates the key events and
dates.
At the conclusion of a five-day trial, the jury reached a
verdict in Seagen’s favor, finding that (1) Daichii failed to
prove any of the asserted claims were invalid, (2) Seagen
proved Daichii’s Enhertu infringed at least one of the as-
serted claims and that such infringement was willful, and
(3) Seagen proved Daichii owed an upfront royalty of
$41,820,000 (based on Daichii’s net revenue during the pe-
riod of infringement) and an 8% running royalty. J.A. 53–
60. Daichii moved for JMOL, arguing, in relevant part,
that (1) the claims were not supported by a sufficient writ-
ten description, (2) the claims were not enabled, and (3)
there was not a logical nexus between the licenses relied
upon by Seagen’s damages expert and the hypothetical ne-
gotiation between Seagen and Daichii in arriving at the 8%
royalty rate. J.A. 2134–65, 2191–96. The district court de-
nied Daichii’s motion for JMOL, J.A. 32–49, and entered
final judgment. J.A. 50–52.
Daichii timely appealed. We have jurisdiction under
28 U.S.C. § 1295(a)(1).
In January 2024, in the separate PGR proceeding, the
Board issued a final written decision holding the claims as-
serted in the district court litigation unpatentable on the
same grounds asserted by Daichii in the district court case.
Daiichi, No. PGR2021-00030, Paper 57. Seagen has ap-
pealed the Board’s decision to this court, which has been
designated as a companion case to the instant appeal, and
which we dismiss as moot in a separate decision. See Sea-
gen Inc. v Daichii Sankyo, Inc. No. 24-1878, slip. op. at 3
(Fed. Cir. 2025).
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SEAGEN INC. v. DAIICHI SANKYO COMPANY , LTD. 9
D ISCUSSION
On appeal, Daichii argues that the district court erred
in denying JMOL on each of the above issues that Daichii
raised in its post-trial briefing; it does not challenge the
jury’s finding that Enhertu infringes at least one claim of
the ’039 patent. Daichii Br. 38–76. Daichii’s liability there-
fore rises and falls with its invalidity arguments. Because
the record does not contain substantial evidence that the
2004 application provides written description support for a
Gly/Phe-only tetrapeptide or that the ’039 patent enables a
skilled artisan to make and use the full scope of the claimed
ADCs without undue experimentation, we conclude that all
of its claims are invalid. We therefore need not reach
Daichii’s challenge to Seagen’s damages award.
We review the denial of a motion for JMOL under re-
gional circuit law. Freshub, Inc. v. Amazon.com, Inc., 93
F.4th 1244, 1249 (Fed. Cir. 2024). JMOL is appropriate
only where “the facts and inferences point so strongly and
overwhelmingly in favor of one party that the court con-
cludes that reasonable jurors could not arrive at a contrary
verdict.” Orion IP, LLC v. Hyundai Motor Am., 605 F.3d
967, 973 (Fed. Cir. 2010) (applying Fifth Circuit law). We
affirm a district court’s denial of judgment as a matter of
law when there was substantial evidence to support the
jury’s verdict. Power-One, Inc. v. Artesyn Techs., Inc., 599
F.3d 1343, 1350–51 (Fed. Cir. 2010) (applying Fifth Circuit
law). Federal Circuit law applies to issues of substantive
patent law. See e.g., Colibri Heart Valve LLC v. Medtronic
CoreValve, LLC, 143 F.4th 1367, 1376 (Fed. Cir. 2025).
I. Written Description
In order for a later-filed patent “to gain the benefit” of
an earlier application’s priority date, inter alia, the earlier
application must disclose an invention “in the manner pro-
vided by section 112(a) [of the Patent Act].” Lockwood v.
Am. Airlines, Inc., 107 F.3d 1565, 1571 (Fed. Cir. 1997); 35
U.S.C. § 120. Section 112(a) of the Patent Act provides that
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SEAGEN INC. v. DAIICHI SANKYO COMPANY , LTD. 10
a patent “specification shall contain a written description
of the invention.” 35 U.S.C. § 112(a). A specification ade-
quately describes an invention when it “reasonably conveys
to those skilled in the art that the inventor had possession
of the claimed subject matter as of the filing date.” Ariad
Pharms., Inc. v. Eli Lilly & Co., 598 F.3d 1336, 1351 (Fed.
Cir. 2010) (en banc) (citation omitted). “[T]he hallmark of
written description is disclosure” in the “four corners of the
specification.” Id. Whether a patent complies with the
written description requirement is a question of fact, and
“we review a jury’s determinations of facts relating to com-
pliance with the written description requirement for sub-
stantial evidence.” Juno Therapeutics, Inc. v. Kite Pharma,
Inc., 10 F.4th 1330, 1335–36 (Fed. Cir. 2021) (quoting Ar-
iad, 598 F.3d at 1355).
Daichii argues that no reasonable jury could have
found that the 2004 application sufficiently discloses the
claimed 81-member subgenus2 of Gly/Phe-only tetrapep-
tides corresponding to the “—Ww— unit” recited in claim 1.
We agree and therefore conclude that substantial evidence
does not support the jury’s finding of adequate written de-
scription.
A
The 2004 application only broadly outlines the possible
structures of the Ww peptide unit that are included in the
linker protein. It states that “when present,” the peptide
unit “Ww” can be any of “a dipeptide, tripeptide, tetrapep-
tide, pentapeptide, hexapeptide, heptapeptide, octapep-
tide, nonapeptide, decapeptide, undecapeptide or
2 We use the term “subgenus” here because the par-
ties have. Claim 1 is of course a subgenus of a larger genus
described in the 2004 application. But claim 1 might
equally be called a genus, as it certainly is, in fact, a rather
large one, as can be seen here.
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SEAGEN INC. v. DAIICHI SANKYO COMPANY , LTD. 11
dodecapeptide unit.” J.A. 5722–23. That is, if the peptide
unit is included in the ADC described in the 2004 applica-
tion, it can include anywhere from two to twelve amino ac-
ids. J.A. 5722–23. The 2004 application then describes 39
different amino acids that can constitute the R19 group,
which determines the identity of the —W— unit. J.A.
5723. When different isomers of the identified amino acids
are included, there are 83 unique options for each “—W—”
unit. See J.A. 3243 (130:16–132:24). Accordingly, just with
respect to tetrapeptides, over 47 million different tetrapep-
tide units (i.e., 83 4) are encompassed in the 2004 applica-
tion.3 Seagen and Daichii’s witnesses agreed on this point
at trial. J.A. 3120 (265:3–10) (lead named inventor Dr. Pe-
ter Senter admitting that “[t]he number of options” in the
2004 application “for just the tetrapeptide category alone
is over 47 million”), 3243 (132:19–24) (Daichii expert Dr.
John Lambert stating that in “[I]n tetrapeptides alone[,]
there are 47 million options” possible in the 2004 applica-
tion).
But such evidence is insufficient to support the jury’s
finding of adequate written description in the 2004 appli-
cation. As we have consistently held, a patent’s disclosure
of a “broad genus,” without more, is inadequate to satisfy
the written description requirement for claims directed to
a “particular subgenus or species contained therein.” See,
e.g., Novozymes A/S v. DuPont Nutrition Biosciences APS,
723 F.3d 1336, 1346 (Fed. Cir. 2013).
Our predecessor court’s decision in In re Ruschig is in-
structive. 379 F.2d 990 (CCPA 1967). There, the claim re-
cited a single compound, which was “encompassed” in the
application’s “general disclosure of . . . something like half
3 The number of peptides encompassed by the 2004
application with each additional amino acid unit grows ex-
ponentially—e.g., almost four billion pentapeptides are in-
cluded (83^5).
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SEAGEN INC. v. DAIICHI SANKYO COMPANY , LTD. 12
a million possible compounds.” Id. at 993, 996. The appli-
cant urged that such a disclosure was adequate. The Court
of Customs and Patent Appeals (“CCPA”) rejected that ar-
gument, explaining that claims to a particular species or
subgenus require “reasonably specific supporting disclo-
sure” to show that the inventor possessed the specific com-
pound. Id. at 994.
Similarly, here, it was undisputed at trial that the 2004
application broadly discloses an extraordinary number of
peptide units—e.g., with respect to just the tetrapeptides
covered, over 47 million species based on 83 different
amino acids. J.A. 3120 (265:3–10), 3243 (132:19–24). And
although the 81 claimed Gly/Phe-tetrapeptides are “encom-
passed” within those 47 million, see J.A. 3148 (46:8–11),
3256–57 (184:23–185:22), they are merely an infinitesimal
fraction of those peptide units generally included. Under
Ruschig, such evidence does not provide “reasonably spe-
cific supporting disclosure” for the claimed subgenus of 81
Gly/Phe-only tetrapeptides. 379 F.2d at 993–94. Accord-
ingly, the above evidence was not substantial evidentiary
support for the jury’s finding of adequate written descrip-
tion.
The ’039 patent thus cannot claim priority from the
2004 application, meaning that the December 2015 public
disclosure of Enhertu, which was found to contain each lim-
itation of at least claim 1 (the sole independent claim), an-
ticipates, and thus invalidates the ’039 patent. Bristol-
Myers Squibb Co. v. Ben Venue Laby’s, Inc., 246 F.3d 1368,
1378 (Fed. Cir. 2001 (“[T]hat which would literally infringe
if later anticipates if earlier.”).
Attempting to distinguish cases like Ruschig, Seagen
principally relies on another of our predecessor court’s de-
cisions, In re Driscoll, 562 F.2d 1245 (CCPA 1977). Seagen
Br. 35–36. There, the patent claim recited a subgenus of
chemical compounds with a specific moiety, and an earlier
application which the patent claimed priority from recited
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SEAGEN INC. v. DAIICHI SANKYO COMPANY , LTD. 13
fourteen moieties, including the one claimed. Driscoll, 562
F.2d at 1249. The CCPA held that the earlier application
provided written description support for the claim because
“the exact subgenus claimed is clearly discernible in the
generalized formula” and therefore “a skilled artisan would
recognize from the disclosure of [the specification]” that the
inventor possessed each of the “fourteen distinct [moie-
ties].” Id. at 1249–50.
Seagen’s reliance on Driscoll is misplaced. Here, as
discussed, there are effectively countless peptide units en-
compassed by the 2004 application—a far cry from the 14
moieties individually listed in the specification in Driscoll.
And the claimed subgenus of 81 Gly/Phe-only tetrapeptides
is never mentioned in the 2004 application, and therefore
is not “clearly discernible in the generalized formula” in the
way the CCPA found sufficient in Driscoll. Id. at 1250.
The conclusion that the 2004 application does not pro-
vide adequate written description support is further sup-
ported by admissions from the ’039 patent’s named
inventors that they had never contemplated an ADC with
a Gly/Phe-only tetrapeptide as of the 2004 application’s pri-
ority date. See Nuvo Pharms. (Ireland) Designated Activity
Co. v. Dr. Reddy’s Lab’ys Inc., 923 F.3d 1368, 1381 (Fed.
Cir. 2019) (inventor testimony can “illuminate[] the ab-
sence of critical [written] description”).
Specifically, lead inventor Dr. Senter admitted that the
“first time . . . [he] ever saw a G/F-only tetrapeptide in an
ADC . . . was in Dacihii Sankyo’s Enhertu,” which was pub-
licly disclosed in 2015. J.A. 3119 (261:22–23). Similarly,
inventor Dr. Svetlana Doronina admitted that “the claims
of the ’039 patent,” filed in 2019, were “the first time” she
had “seen described a genus of tetrapeptide linkers that’s
limited to glycine [and] phenylalanine.” J.A. 3295 (74:9–
12). Named inventors Dr. Brian Toki and Dr. Toni Kline
testified to similar effect. J.A. 3292 (62:13–63:4) (Dr. Toki);
3297 (84:1–9). Because “one cannot describe what one has
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SEAGEN INC. v. DAIICHI SANKYO COMPANY , LTD. 14
not conceived,” Fiers v. Revel, 984 F.2d 1164, 1171 (Fed.
Cir. 1993), the inventors’ admissions bolster the conclusion
that they did not possess the claimed subgenus of Gly/Phe-
only tetrapeptides as of the November 2004 priority date.
Dr. Senter’s additional testimony that the inventors
created ADC linkers comprising “almost any peptide” prior
to the 2004 application’s priority date is not sufficient to
overcome his above admission for the same reason that the
disclosures in the 2004 application are inadequate. Seagen
Br. 38 n.12; J.A. 3110 (229:6–8). Dr. Senter’s testimony
does not show that the 2004 application provides “reason-
ably specific supporting disclosure” for the claimed
Gly/Phe-only tetrapeptides, or that the inventors had pos-
session of that subgenus of tetrapeptides. Ruschig, 379
F.2d at 994.
B
Separately, Seagen asserts that the finding of adequate
written description was supported by substantial evidence
because the jury heard testimony that the 2004 application
would “direct[]” a skilled artisan to the claimed subgenus
of Gly/Phe-only tetrapeptides. Seagen Br. 40–45. We have
often analyzed such theories by analogizing a genus and its
constituent subgenuses or species to a forest and trees:
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 . . . not yet been made
. . . to be confronted simply by a large number of
unmarked trees. . . . We are looking for blaze marks
which single out particular trees.
Ruschig, 379 F.2d at 994–95 (emphasis added).
Seagen presented its “blaze-mark” theory through Dr.
Carolyn Bertozzi. Dr. Bertozzi provided considerable tes-
timony purporting to show how a skilled artisan could have
made certain changes in the compounds disclosed to arrive
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SEAGEN INC. v. DAIICHI SANKYO COMPANY , LTD. 15
at a compound within the scope of the claimed subgenus.
Specifically, Dr. Bertozzi testified that, based on the 2004
application’s disclosure of the tetrapeptide, GFLG, to-
gether with several tripeptides where phenylalanine is at
the second position, a skilled artisan would understand
that “F at [position] 2” was a possible substitution for leu-
cine in GFLG. J.A. 3299–3300 (91:19–93:5). The highlight
of that testimony stated that it would be a “straightforward
leap” for a skilled artisan “to go from GFLG . . . to a
[tetra]peptide that’s all G and F.” J.A. 3149 (50:25–51:2).
But that testimony dooms Seagen’s case. That which
one must leap to is obviously not there. It is thus axiomatic
that a skilled artisan need not make a “leap” to “a
[tetra]peptide that’s all G and F” if the skilled artisan were
to understand that the 2004 application itself disclosed
such a peptide. J.A. 3149 (50:25–51:2). That testimony is
accordingly self-defeating: It in effect admits that a skilled
artisan would not understand the inventors of the 2004 ap-
plication to have “possession” of GFFG. Ariad, 598 F.3d at
1351; see also Lockwood, 107 F.3d at 1572. (“It is not suf-
ficient for purposes of . . . written description . . . that the
disclosure, when combined with the knowledge in the art,
would lead one to speculate as to modifications that the in-
ventor might have envisioned, but failed to disclose.”); Re-
gents of the Univ. of Minn. v. Gilead Scis. Inc., 61 F.4th
1350, 1358 (Fed. Cir. 2023) (lack of written description
where the priority documents blaze a trail “that runs close
by the later-claimed tree,” but “‘do[ ] not direct one to the
proposed tree in particular, and do[ ] not teach the point at
which one should leave the trail to find it.’” (alterations in
original) (quoting Fujikawa v. Wattanasin, 93 F.3d 1559,
1571 (Fed. Cir. 1996))).
In sum, the 2004 application’s broad disclosure of effec-
tively countless options for the peptide unit fails to show
the subgenus of Gly/Phe-only tetrapeptides claimed in the
’039 patent. Moreover, there are no adequate blaze marks
that would lead a skilled artisan to the 81-member
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SEAGEN INC. v. DAIICHI SANKYO COMPANY , LTD. 16
Gly/Phe-only tetrapeptide subgenus or any species within
it. A reasonable jury therefore did not have sufficient evi-
dence to find that the ’039 patent provided written descrip-
tion support for what it claimed. Accordingly, the district
court erred in denying Daichii’s motion for JMOL on that
ground.
II. Enablement
Another issue at trial relating to validity was whether
the ’039 patent satisfied the enablement requirement. Spe-
cifically, the parties disputed whether the ’039 patent suf-
ficiently enabled a skilled artisan to make and use ADCs
with the claimed structure and function. Seagen’s wit-
nesses asserted that undue experimentation was not nec-
essary to make and use the full scope of claimed ADCs.
The enablement requirement is distinct from the writ-
ten description requirement. Ariad, 598 F.3d at 1351. A
patent’s specification must describe the invention and “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 . . . to make and use
the same.” 35 U.S.C. § 112(a). This means that “the spec-
ification must enable the full scope of the invention as de-
fined by its claims,” allowing for “a reasonable amount of
experimentation.” Amgen v. Sanofi, 598 U.S. 594, 610, 612
(2023). Put differently, “[t]o be enabling, the specification
of a patent must teach those skilled in the art how to make
and use the full scope of the claimed invention without un-
due experimentation.” MagSil Corp. v. Hitachi Glob. Stor-
age Techs., Inc., 687 F.3d 1377, 1380 (Fed. Cir. 2012)
(cleaned up). “Whether a claim satisfies § 112’s enable-
ment requirement is a question of law [that] we review de
novo; however, in the context of a jury trial, we review the
factual underpinnings of enablement for substantial evi-
dence.” Trs. of Bos. Univ. v. Everlight Elecs. Co., 896 F.3d
1357, 1361 (Fed. Cir. 2018) (citation omitted).
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SEAGEN INC. v. DAIICHI SANKYO COMPANY , LTD. 17
Daichii argues that the ’039 patent failed to provide an
enabling disclosure of the subject matter of the claims. We
agree with Daichii. No reasonable jury could have found
that the specification of the ’039 patent teaches a skilled
artisan how to make and use the full scope of the claimed
invention. We therefore conclude that substantial evidence
does not support the jury’s finding of enablement for any of
the asserted claims.
The Supreme Court’s decision in Amgen v. Sanofi,
unanimously affirming our decision, is relevant here. In
Amgen, the patents claimed “the entire genus of antibod-
ies” that (1) bind to specific amino acid residues on a pro-
tein and (2) block that protein from binding to receptors
involved in removing a certain harmful cholesterol from
the bloodstream. 598 U.S. at 602 (internal quotations
omitted). It was undisputed that the claims covered “at
least millions” of antibodies with the recited functionali-
ties. Id. at 613. The patents’ specification identified 26
antibodies that perform the two recited functions along
with their relevant structures, id. at 602–03, as well as two
methods for testing whether a particular antibody per-
forms the two recited functions. Id. at 603.
Amgen, the patent owner, contended that the specifi-
cation’s disclosure of the two methods was sufficient to en-
able a skilled artisan to make and use the full scope of the
claimed invention. Id. at 613–14. The Court rejected that
argument. It explained that—in light of the unpredictabil-
ity of antibody science where even a minor change of chem-
ical structure can alter an antibody’s functionality—
without disclosing “a quality common to every functional
embodiment,” both methods effectively amounted to telling
a skilled artisan to perform “trial-and-error discovery” to
determine if any one antibody may possess the recited
functionalities. Id. at 600, 614–15.
So too here. The district court construed the limitation
“D is a drug moiety” to encompass any type of drug moiety.
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SEAGEN INC. v. DAIICHI SANKYO COMPANY , LTD. 18
J.A. 1287–92. Further, the ’039 patent recites a functional
limitation: “the drug moiety is intracellularly cleaved in a
patient from the antibody.” ’039 patent col. 332 ll. 37–39;
see Nevro Corp. v. Bos. Sci. Corp., 955 F.3d 35, 39 (Fed. Cir.
2020) (“[A] functional term [is] defined by what it does ra-
ther than what it is.”). Taken together, these two limita-
tions mean that the ’039 patent covers an ADC containing
any drug moiety with the recited function of cleaving in a
patient. But the specification does not disclose “a quality
common to every functional embodiment” of the patent.
Amgen, 598 U.S. at 614. Rather, it is undisputed that ADC
science was so unpredictable that a skilled artisan would
be required to use an assay to test whether any given ADC
with a given drug moiety meets that functional limitation.
J.A. 3296 (78:21–79:1) (inventor Dr. Kline admitting that a
skilled artisan would need to conduct an assay to deter-
mine whether a given ADC is “is going to be successfully
intracellularly cleaved”); Seagen Br. 56–57 (listing various
assays a skilled artisan would know to use to determine
whether a given ADC’s drug moiety is intracellularly
cleaved). Therefore, just as in Amgen, a skilled artisan
would be left to perform far-ranging “trial-and-error discov-
ery” to make and use the ADCs within the scope of the ’039
patent. Amgen, 598 U.S. at 615.4 Under these circum-
stances, where the scale of trial and error is so vast and the
science so unpredictable, such experimentation is undue
under Amgen, see id. Thus, the jury did not have substan-
tial evidence to conclude that the ’039 patent was enabled.
4 The amount of trial-and-error discovery that would
be required to determine whether an ADC with a given
drug intracellularly cleaves is further increased by the
need to test each ADC with the recited structural limita-
tions.
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SEAGEN INC. v. DAIICHI SANKYO COMPANY , LTD. 19
CONCLUSION
We have considered Seagen’s remaining arguments
and find them unpersuasive. For the foregoing reasons, we
reverse the district court’s denial of judgment as a matter
of law that the ’039 patent is not invalid for failure to meet
the written description and enablement requirements. The
’039 patent is therefore invalid. We vacate the jury’s find-
ing of willful infringement and assessment of damages.
REVERSED
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