United States Court of Appeals 

for the Federal Circuit 

__________________________ 

CANCER RESEARCH TECHNOLOGY LIMITED 

AND SCHERING CORPORATION, 

Plaintiffs-Appellants, 

v. 

BARR LABORATORIES, INC. AND 

BARR PHARMACEUTICALS, INC., 

Defendants-Appellees. 

__________________________ 

2010-1204 

__________________________ 

Appeal from the United States District Court for the 

District of Delaware in Case No. 07-CV-0457, Judge Sue 

L. Robinson. 

____________________________ 

Decided: November 9, 2010 

____________________________ 

MATTHEW D. POWERS, Weil Gotshal & Manges LLP, of 

Redwood Shores, California, argued for plaintiffsappellants. With him on the brief were NICOLAS G.

BARZOUKAS and JASON C. ABAIR, of Houston, Texas; and 

JENNIFER H. WU, of New York, New York. 

GEORGE C. LOMBARDI, Winston & Strawn LLP, of Chicago, Illinois, argued for defendants-appellees. With him 

on the brief were LYNN M. ULRICH, MAUREEN L. RURKA, 
CANCER RESEARCH v. BARR LABS 2

IVAN M. POULLAOS, and JULIA MANO JOHNSON. Of counsel 

on the brief was STEFFAN N. JOHNSON, of Washington, 

DC. 

__________________________ 

Before NEWMAN, LOURIE, and PROST, Circuit Judges. 

Opinion for the court filed by Circuit Judge LOURIE, in 

which Circuit Judge NEWMAN joins. 

Dissenting opinion filed by Circuit Judge PROST. 

LOURIE, Circuit Judge. 

Cancer Research Technology Limited and Schering 

Corporation (collectively, “Cancer Research”) appeal from 

the final decision of the United States District Court for 

the District of Delaware holding U.S. Patent 5,260,291 

(“the ’291 patent”) unenforceable for prosecution laches 

and inequitable conduct. Cancer Research Tech. v. Barr 

Labs., Inc., 679 F. Supp. 2d 560 (D. Del. 2010). We reverse. 

BACKGROUND

The ’291 patent claims a genus of tetrazine derivative 

compounds and methods for treating cancer by administering those compounds. One claimed compound, temozolomide, is the active ingredient in the drug Temodar®, 

approved by the Food and Drug Administration (“FDA”) 

for the treatment of two types of brain cancer—refractory 

anaplastic astrocytoma and newly diagnosed glioblastoma 

multiforme. 

The application for the ’291 patent was filed in the 

United States on August 23, 1982, by a British pharmaceutical company. The original specification identifies 

and characterizes thirteen “[i]mportant” tetrazine derivative compounds, designated A through M, and it identifies 

three of the thirteen compounds, including temozolomide 
3 CANCER RESEARCH v. BARR LABS

(designated as A) and mitozolomide (designated as C), as 

having “particular importance.” ’291 patent col.4 l.57, 

col.5 ll.17-18. The specification states that the new 

tetrazine derivatives “possess valuable antineoplastic 

activity, for example against carcinomas, melanomas, 

sarcomas, lymphomas and leukaemias” and “have proved 

particularly active” in several different mouse tumor 

models. Id. col.4 ll.29-56. The specification goes on to 

disclose positive data from those animal models. Id.

In the first substantive office action dated November 

18, 1983, the examiner, Examiner Ford, rejected original 

claim 31 directed to a method of treating leukemia by 

administering a tetrazine compound because “[t]he treatment of leukaemia is not a believable utility on its face” 

and objected to the composition claims “pending clarification of utility.” A2394-96. The examiner wrote that 

utility could be established “by clinical reports and data, 

the acceptance of the drug employed by the Food and 

Drug Administration and by the American Medical Association Council on Pharmacy,” citing Ex parte Timmis, 

123 U.S.P.Q. 581 (POBA 1959). A2395. The applicants 

did not respond to the office action but instead filed a 

continuation application on March 6, 1984, and abandoned the original application. On October 24, 1984, 

Examiner Ford again rejected claim 31 for lack of utility 

and objected to the composition claims pending clarification of utility. Again, the applicants, rather than respond 

to the office action, filed a continuation application and 

abandoned the pending application. This pattern repeated itself eight more times, with the examiner ultimately rejecting all the pending claims for lack of utility. 

On March 25, 1991, ownership of the patent application changed hands, with Cancer Research receiving an 

absolute assignment of rights. On October 18, 1991, 

Cancer Research filed another continuation application, 
CANCER RESEARCH v. BARR LABS 4

but for the first time challenged the examiner’s utility 

rejection, arguing that the disclosure of animal data in 

the original specification sufficed to establish utility in 

humans. In the next office action, a new examiner, Examiner Richter, modified the utility rejection, stating that 

the disclosure established utility but only for claims 

limited to the specific antineoplastic activity listed and 

tested in the specification. In response, Cancer Research 

again argued patentability based on the animal testing 

disclosed in the original specification, relying on a quote 

from In re Buting, 418 F.2d 540 (CCPA 1969), that 

“[s]ubstantiating evidence may be in the form of animal 

tests which constitute recognized screening procedures 

with clear relevance to utility in humans.” A2086. Subsequently, a third examiner, Examiner Dentz, found the 

claims allowable, and the ’291 patent issued on November 

9, 1993. 

During the prosecution of the ’291 patent, the applicants continued to study tetrazine derivatives as a treatment for cancer, and inventor Dr. Malcolm Stevens coauthored numerous articles reporting both animal and 

human clinical data to the scientific community. One of 

the tetrazine compounds described in the ’291 patent as 

having “particular importance,” mitozolomide, showed 

broad spectrum antitumor activity in mice and was advanced to human clinical trials in 1983. Phase I and II 

human trials showed mitozolomide to have toxic side 

effects and little activity against many cancers. In light of 

mitozolomide’s toxic side effects, further studies with the 

compound were halted. Instead, a second tetrazine compound of “particular importance,” temozolomide, entered 

Phase I human testing in 1987. By 1989, reports showed 

that temozolomide was safe and had some anti-cancer 

activity. Clinical testing of temozolomide continued after 

the issuance of the ’291 patent, and the FDA approved 
5 CANCER RESEARCH v. BARR LABS

Temodar® for the treatment of refractory anaplastic 

astrocytoma in August 1999, and for the treatment of 

newly diagnosed glioblastoma multiforme in March 2005. 

In October 1999, Schering Corp., the new exclusive licensee under the patent, filed for a patent term extension 

under 35 U.S.C. § 156, which added 1,006 days to the ’291 

patent’s term. The patent also was granted a pediatric 

exclusivity period and will expire in February 2014. 

On March 19, 2007, Barr Laboratories, Inc. and Barr 

Pharmaceuticals, Inc. (collectively, “Barr”) filed an Abbreviated New Drug Application (“ANDA”) with a Paragraph 

IV certification under the Hatch-Waxman Act, 21 U.S.C. 

§ 355, challenging the validity of the ’291 patent and 

seeking FDA approval for generic Temodar®. Cancer 

Research sued Barr for patent infringement in the United 

States District Court for the District of Delaware on July 

20, 2007. The parties stipulated to infringement and 

validity of claim 13 directed to temozolomide, leaving only 

Barr’s counterclaims that the patent was unenforceable 

for prosecution laches and for inequitable conduct. 

After a bench trial, the district court held the ’291 

patent unenforceable for prosecution laches. The district 

court first decided that under Symbol Technologies, Inc. v. 

Lemelson Medical, 422 F.3d 1378 (Fed. Cir. 2005) (“Symbol Techs. II”), prosecution laches did not require a showing of intervening rights but rather turned on whether 

under the totality of the circumstances Cancer Research’s 

delay in prosecution in light of the PTO’s utility rejections 

was unreasonable and unexplained. Cancer Research, 

679 F. Supp. 2d at 572-73. The court then found that 

even assuming, as Cancer Research claimed, that the 

PTO’s rejections required the submission of human clinical data to establish utility in humans, and thus patentability, Cancer Research could have attempted to 

traverse the rejection based on then-existing case law 
CANCER RESEARCH v. BARR LABS 6

holding that such utility could be shown by animal tests, 

but waited until doing so benefited it commercially. Id. at 

574. Furthermore, according to the district court, even if 

the examiner had rejected Cancer Research’s position, a 

subsequent office action would have at the very least 

clarified the examiner’s position on the need for human 

data without putting the company in a worse position. Id. 

The district court thus held that the delay caused by 

eleven continuation applications, ten abandonments, and 

no substantive prosecution for nearly a decade was unreasonable and a sufficiently egregious misuse of the patent 

system to bar enforcement of the ’291 patent for prosecution laches. Id. at 575. 

The district court also held the ’291 patent unenforceable for inequitable conduct. The court first found that 

Cancer Research failed to disclose highly material information to the PTO. Specifically, the court found that 

Cancer Research did not disclose Phase I and II human 

data indicating that mitozolomide failed to treat numerous cancers covered by the ’291 patent claims and did not 

disclose other data indicating that the inventors considered other claimed tetrazine compounds to be inactive in 

at least one cancer model. Id. at 580. The district court 

found this withheld information to be highly material 

because it directly contradicted statements in the ’291 

patent regarding the compounds’ broad utility in treating 

cancers and directly contravened the patentability of 

broadly written claim 28. Id. at 580-81. In so finding, the 

court rejected Cancer Research’s arguments that the 

Phase I data were not material because they focused on 

safety rather than efficacy and that the Phase II data 

were not material because they were preliminary and 

inconclusive. The court found that those arguments were 

belied by inventor Stevens’s widespread publication of the 

data. Id. at 580. The district court also rejected Cancer 
7 CANCER RESEARCH v. BARR LABS

Research’s argument that other undisclosed studies were 

positive and supported the utility of the claims, concluding that the nondisclosure of positive data did not mitigate the fact that Cancer Research withheld negative 

data or its finding that the negative data were highly 

material. Id. at 581. 

The district court next found that inventor Stevens 

withheld the data with intent to deceive because (1) the 

withheld information was highly material, (2) Stevens 

knew about the information and should have appreciated 

its materiality as it directly contradicted the application’s 

disclosure, and (3) Stevens did not provide a credible 

explanation for withholding the information. Id. With 

regard to the latter, the district court found not credible 

Stevens’s testimony that he considered the withheld data 

to be confidential to clinicians and inconclusive in view of 

Stevens’s widespread publication both of the data and of 

his conclusions that the data showed the compounds to be 

inactive and toxic. Id. The district court also found 

Stevens’s publication of the withheld data a sufficient 

basis upon which to infer intent to deceive. Id. at 582. 

The district court entered final judgment in favor of 

Barr on January 29, 2010, and Cancer Research appealed. 

We have jurisdiction pursuant to 28 U.S.C. § 1295(a)(1). 

DISCUSSION

I. Prosecution Laches 

Prosecution laches is an equitable defense to a charge 

of patent infringement. Symbol Techs., Inc. v. Lemelson 

Med., 277 F.3d 1361, 1366 (Fed. Cir. 2002) (“Symbol 

Techs. I”). The doctrine “may render a patent unenforceable when it has issued only after an unreasonable and 

unexplained delay in prosecution” that constitutes an 

egregious misuse of the statutory patent system under the 
CANCER RESEARCH v. BARR LABS 8

totality of the circumstances. Symbol Techs. II, 422 F.3d 

at 1385-86. We review a district court’s determination of 

prosecution laches for abuse of discretion, id. at 1384, but 

we review the legal standard applied by the district court 

de novo, IPXL Holdings, L.L.C. v. Amazon.com, Inc., 430 

F.3d 1377, 1380 (Fed. Cir. 2005). 

Cancer Research first argues that the district court 

erred as a matter of law in holding the ’291 patent unenforceable for prosecution laches because the court failed to 

find any evidence of actual prejudice either to the defendant, Barr, or to the public. Cancer Research argues that 

prosecution laches is a limited doctrine that only applies 

to bar enforcement of a patent when an applicant purposely delays prosecution in an attempt to cover technology that has already been exploited by others who have no 

knowledge of the patent. In other words, according to 

Cancer Research, the doctrine of prosecution laches 

requires both an unreasonable and unexplained delay in 

prosecution and prejudice based on the intervening rights 

of the defendant or the public during the period of delay. 

Alternatively, Cancer Research argues that the district 

court erred in finding that it unreasonably delayed prosecution of the ’291 patent because it did not deliberately 

seek to delay the patent’s issuance or the public’s access 

to Temodar®, but rather filed continuations based on a 

good faith belief that conclusive human clinical data were 

required to overcome the PTO’s utility rejections. 

Barr responds that the district court correctly held 

the ’291 patent unenforceable due to prosecution laches. 

Barr first argues that the district court correctly recognized that the defense of prosecution laches does not 

require a specific showing of prejudice. Rather, Barr 

suggests that an unreasonable and unexplained delay in 

prosecution inherently prejudices the public if, as here, 

the delay extends the patent monopoly into the future, 
9 CANCER RESEARCH v. BARR LABS

thus preventing Barr’s earlier entry into the market for 

temozolomide. Barr also argues that the district court 

correctly found that the applicants unreasonably delayed 

prosecution. Specifically, Barr contends that it was 

unreasonable to file identical continuation applications, 

abandonments, and requests for extension of time for nine 

years without any attempt to substantively advance 

prosecution until it became commercially advantageous to 

do so. Furthermore, Barr argues that Cancer Research 

offers no credible justification for the nine-year delay. 

According to Barr, Cancer Research’s alleged belief that 

clinical human data were required to overcome the PTO’s 

utility rejections not only ignores pre-1982 case law 

holding that animal data can establish the human utility 

of anti-cancer compounds, but also is belied by the applicants’ use of animal data to secure issuance of the ’291 

patent and by their failure to submit human data to the 

PTO as such data became available during prosecution. 

We agree with Cancer Research that prosecution laches’ requirement of an unreasonable and unexplained 

delay includes a finding of prejudice, as does any laches 

defense. See A.C. Aukerman Co. v. R.L. Chaides Const. 

Co., 960 F.2d 1020, 1028 (Fed. Cir. 1992) (“Two elements 

underlie the defense of laches: (a) the patentee’s delay in 

bringing suit was unreasonable and inexcusable, and (b) 

the alleged infringer suffered material prejudice attributable to the delay.”). We also agree and now hold that to 

establish prejudice an accused infringer must show evidence of intervening rights, i.e., that either the accused 

infringer or others invested in, worked on, or used the 

claimed technology during the period of delay. 

The Supreme Court cases underlying the doctrine all 

rely on a finding that the applicant’s delay in prosecution 

adversely affected others working in the same field. In 

Woodbridge v. United States, applicant Woodbridge 
CANCER RESEARCH v. BARR LABS 10

delayed the issuance of his patent after allowance by 

requesting that the PTO keep it secret in its archives as 

the then-governing patent statute permitted for a term 

not to exceed one year. 263 U.S. 50, 52-53 (1923). Nine 

and a half years later, Woodbridge requested that the 

patent issue because the technology had become commercially profitable. Id. at 53, 56. He also requested that his 

specification and claims be broadened to cover related 

innovations that others had patented in the intervening 

years. Id. at 53, 57. The Court held that Woodbridge had 

forfeited his right to his patent by “designed delay,” and 

specifically by attempting, for the admitted purpose of 

capturing the most commercial profit, to extend both the 

term of his patent monopoly and its scope to cover advances made by others in the field who had obtained 

patents without knowledge of Woodbridge’s patent. Id. at 

56-57. 

Similarly in Webster Electric Co. v. Splitdorf Electrical 

Co., 264 U.S. 463 (1924), the Court again relied on both 

an unreasonable delay and intervening adverse rights to 

hold a patent forfeited for prosecution laches. In Webster, 

the applicant filed new and broader claims in a divisional 

application over eight years after his original application 

was filed. Yet during the eight-year delay, the subject 

matter of those new and broader claims had been disclosed and had come to be in general use while the applicant and his assignee “simply stood by and awaited 

developments.” Id. at 465. In holding that the delay was 

unreasonable and thus constituted laches, the Court 

concluded that the patent law should not be so loosely 

construed as to “bring about an undue extension of the 

patent monopoly against private and public rights.” Id. at 

466 (emphasis added). 

The Court’s last pronouncements on prosecution laches in Crown Cork & Seal Co. v. Ferdinand Gutmann 
11 CANCER RESEARCH v. BARR LABS

Co., 304 U.S. 159 (1938), and General Talking Pictures 

Corp. v. Western Electric Co., 304 U.S. 175 (1938), also 

relied on a requirement for intervening rights. In both 

cases the Court held that in the absence of intervening 

rights, no excuse is necessary for a delay in presenting 

new claims in a continuation or divisional application. 

Crown Cork, 304 U.S. at 167-68 (“It is clear that, in the 

absence of intervening adverse rights, the decision in 

Webster, . . . does not mean that an excuse must be shown 

for a lapse of more than two years in presenting the 

divisional application.”); Gen. Talking Pictures, 304 U.S. 

at 183 (“In the absence of intervening adverse rights for 

more than two years prior to the [filing of new claims in] 

continuation applications, they were [filed] in time.”). 

This court’s precedent also recognizes intervening adverse rights as a requirement to holding a patent unenforceable for prosecution laches. In first recognizing the 

doctrine, we relied on the above-cited Supreme Court 

cases and noted their reliance on intervening rights. 

Symbol Techs. I, 277 F.3d at 1364-65. For example, we 

stated that in Crown Cork, “the [Supreme C]ourt ratified 

the existence of the prosecution laches defense; it did not 

apply the defense there in the absence of intervening 

rights,” and we noted that “in General Talking Pictures, 

the Court rejected the defense of prosecution laches 

because there was no evidence of intervening public 

rights.” Id. at 1365. We then applied the doctrine in a 

manner that recognized the requirement for intervening 

rights. We held that the district court had not abused its 

discretion in holding certain patents unenforceable for 

prosecution laches based on the applicant’s unreasonable 

delay and “the existence of ‘intervening private and public 

rights.’” Symbol Techs. II, 422 F.3d at 1386. We also 

extended the holding to all the remaining claims based on 

finding that the subject matter of all the asserted patents 
CANCER RESEARCH v. BARR LABS 12

had been pending for eighteen to thirty-nine years, an 

unreasonably long time, and that “prejudice to the public 

as a whole has been shown here in the long period of time 

during which parties, including the [declaratory judgment] plaintiffs, have invested in the technology described 

in the delayed patents.” Id. 

In re Bogese, 303 F.3d 1362 (Fed. Cir. 2002), is not to 

the contrary. In Bogese, we upheld the PTO’s forfeiture 

decision after an applicant filed twelve continuation 

applications over eight years without presenting any 

substantive amendments to traverse an outstanding 

obviousness rejection. Id. at 1363-64. In upholding the 

examiner’s decision that the applicant had forfeited his 

right to the patent, the Board relied on both an unreasonable delay and intervening rights. Regarding the latter, 

the Board found that documentation filed with the PTO 

before the period of delay showed that “the applicant was 

keenly aware, . . . that [articles] embodying [his] invention were being developed and exploited commercially in 

the market place.” Id. at 1366. On appeal, Bogese did not 

challenge the PTO’s decision based on the facts of his 

case, but rather challenged the PTO’s authority to require 

applicants to advance prosecution. Id. at 1369. We 

upheld the PTO’s authority to sanction undue delay under 

the Administrative Procedure Act, 5 U.S.C. § 706, as not 

arbitrary, capricious, or contrary to law. Id. at 1367-69. 

The court did not discuss intervening rights in its opinion, 

as it did not need to, but the PTO relied on the existence 

of intervening rights in its decision in that case. 

Barr’s argument that the public was inherently 

prejudiced by Cancer Research’s delay is not persuasive. 

Cancer Research maintains that it could not have developed temozolomide until Schering agreed to become its 

licensee, after which Schering filed an Investigational 

New Drug Application (“IND”) only one month after the 
13 CANCER RESEARCH v. BARR LABS

issuance of the ’291 patent. An inventor is not obligated 

to develop its product at any particular time prior to 

issuance or within the patent’s term, but, once its patent 

issued and it had a licensee, it filed its IND promptly. Its 

product was approved for marketing in 1999. 

Barr, on the other hand, while entitled under the law 

to file an ANDA four years after the NDA approval, in 

this case in 2003, did not do so until 2007. Thus, Barr 

filed its ANDA more than thirteen years after the issuance of Cancer Research’s patent and more than seven 

years after approval of Cancer Research’s product. Barr 

was thus hardly prejudiced by the delay in the issuance of 

the ’291 patent, in 1993. Nor was anyone else. There has 

been no evidence presented that anyone was deterred 

from entering the market for temozolomide because 

Cancer Research’s patent issued in 1993 rather than 

several years earlier. Thus, the delay had only limited 

consequences to Barr and the public. 

Cancer Research’s delay in prosecuting and issuing its 

patent application, whatever the asserted justifications, 

and we do not appraise them here, caused it to run the 

risk that some other pharmaceutical company (e.g., Barr) 

would intervene and claim prejudice from the delay, but 

that did not happen. Moreover, a consequence of Cancer 

Research’s delay in prosecuting its patent is that it did 

not get the full patent term extension allowed under 35 

U.S.C. § 156 because of the fourteen-year cap on exclusivity when a patent has been extended under the HatchWaxman Act. Id. § 156(c)(3). Thus, rather than having 

consequences for Barr and the public by its delay, Cancer 

Research incurred a cost to its own patent term. 

Finally, we note that the facts of this case are not 

likely to be frequently repeated, as patent terms are now 

measured from effective filing date, id. § 154(c)(1), subject 
CANCER RESEARCH v. BARR LABS 14

to only limited extensions provided by statute, not by 

delaying issuance by refiling. And, it also should be noted 

that, when one considers the public interest, the public 

has benefited here by the fact that Cancer Research did 

develop and market temozolomide, induced by the protection of its patent. Cancer Research should not lose that 

protection because its patent issuance was delayed under 

circumstances where no one suffered prejudice. 

In sum, both the Supreme Court and our cases establish that evidence of intervening rights is required to 

establish “an unreasonable and unexplained delay in 

prosecution.” Symbol Techs. II, 422 F.3d at 1385. Barr 

has failed to establish either that it or that others developed or invested in temozolomide or any other claimed 

tetrazine compound between 1982 and 1991, the period of 

delay. Accordingly, Barr cannot establish prosecution 

laches as a matter of law, and we reverse the decision of 

the district court. 

Because we conclude that the district court committed 

legal error in holding the ’291 patent unenforceable for 

prosecution laches in the absence of any evidence of 

intervening rights, we need not decide if Cancer Research’s delay in prosecuting the ’291 patent was unreasonable or unexplained. 

II. Inequitable Conduct 

The district court also held the ’291 patent unenforceable for inequitable conduct. Cancer Research, 679 F. 

Supp. 2d at 577-82. To successfully prove inequitable 

conduct, the accused infringer must provide evidence that 

the applicant (1) made an affirmative misrepresentation 

of material fact, failed to disclose material information, or 

submitted false material information, and (2) did so with 

intent to deceive the PTO. Star Scientific, Inc. v. R.J. 

Reynolds Tobacco Co., 537 F.3d 1357, 1365 (Fed. Cir. 
15 CANCER RESEARCH v. BARR LABS

2008). Both materiality and intent must be proven by 

clear and convincing evidence. Id. While deceptive intent 

can be inferred from indirect and circumstantial evidence, 

that “inference must not only be based on sufficient 

evidence and be reasonable in light of that evidence, but it 

must also be the single most reasonable inference able to 

be drawn from the evidence to meet the clear and convincing standard.” Id. at 1366. 

This court reviews a district court’s determination of 

inequitable conduct under a two-tiered standard; we 

review the underlying factual determinations of materiality and intent for clear error, and we review the ultimate 

decision as to inequitable conduct for an abuse of discretion. Id. at 1365. If the district court’s inequitable conduct determination rests on a clearly erroneous finding of 

materiality and/or intent, it constitutes an abuse of discretion and must be reversed. Id. 

Cancer Research alleges that, inter alia, the district 

court erred in finding that inventor Stevens withheld 

studies on tetrazine derivatives with deceptive intent. 

Cancer Research argues that there is no evidence to 

counter Stevens’s testimony that he did not consider the 

withheld data material and that by identifying only 

Stevens’s publication of the data to establish his knowledge of its materiality, the district court erroneously 

relied solely on its finding of materiality to infer deceptive 

intent. Furthermore, Cancer Research argues that Stevens provided a good faith explanation for the nondisclosure, testifying that he honestly and to the best of his 

ability provided all necessary information about the 

claimed compounds and, as a laboratory scientist, believed the clinical data were confidential. Finally, Cancer 

Research asserts that nothing in Stevens’s widespread 

publication of the data evidences wrongful intent, but 

rather the opposite, extreme candor. Accordingly, Cancer 
CANCER RESEARCH v. BARR LABS 16

Research concludes that the district court’s inference of 

deceptive intent is far from the single most reasonable 

inference to draw from the evidence, and thus the court’s 

determination of inequitable conduct must be reversed. 

In response, Barr defends the district court’s finding 

of intent. Specifically, Barr argues that, based on Stevens’s testimony at trial, the district court correctly found 

that Stevens knew he possessed undisclosed data that 

contradicted the disclosure in the patent application and 

knew he had a duty to disclose such material information 

to the PTO but did not do so. According to Barr, the only 

reasonable inference to draw from this evidence is an 

intent to deceive. Moreover, Barr argues that the district 

court found Stevens’s explanations for his failure to 

disclose the information not credible, concluding that 

Stevens’s publication of the data along with statements 

regarding the compounds’ “inactivity” and “toxicity” belied 

his assertions that he believed the data to be “inconclusive” and “confidential.” Finally, Barr argues that, contrary to Cancer Research’s contention, the district court 

did not clearly err in finding that Stevens’s publication of 

the withheld data was relevant to intent; the publications 

demonstrate that Stevens’s stated reasons for not disclosing the data were untrue. 

We agree with Cancer Research that the district court 

clearly erred in finding that Stevens intended to deceive 

the PTO by not disclosing data on the claimed compounds, 

and specifically we agree that the district court erred 

because it relied solely on its finding of materiality to 

infer intent. The district court found that “Stevens should 

have appreciated the materiality of the data . . . as they 

expressly contradicted the disclosure of the pending 

applications” and that under the circumstances “Stevens’ 

publications to the scientific community [provided] a 

sufficient basis upon which to infer an intent to deceive.” 
17 CANCER RESEARCH v. BARR LABS

Cancer Research, 679 F. Supp. 2d at 581-82. The district 

court, however, relied on the same evidence in finding the 

withheld data to be “highly material”; the court found 

that “the withheld information directly contradicts statements made in the ’291 patent’s specification,” making it 

highly material, and rejected Cancer Research’s arguments regarding materiality as “belied by the fact that 

Stevens . . . thought the data [were] significant enough to 

describe in publications to the scientific community.” Id.

at 580-81. Because the district court did not rely on any 

other evidence to support its finding of deceptive intent 

beyond that used to find the withheld data material, the 

court in effect relied solely on its materiality finding to 

infer intent to deceive. 

But materiality and intent are separate requirements, 

and intent to deceive cannot be found based on materiality alone. Larson Mfg. Co. of S.D., Inc. v. Aluminart 

Prods. Ltd., 559 F.3d 1317, 1340 (Fed. Cir. 2009). A court 

cannot simply infer that an applicant “should have 

known” the materiality of withheld information and thus 

intended to deceive the PTO because the applicant knew 

of the information and the information is material. A 

district court must find some other evidence that indicates that the applicant appreciated the information’s 

materiality. See, e.g., Critikon, Inc. v. Becton Dickinson 

Vascular Access, Inc., 120 F.3d 1253, 1256 (Fed. Cir. 1997) 

(finding intent to deceive based in part on handwritten 

notes of prosecution counsel corroborating that counsel 

subjectively believed the undisclosed patent was material). In this case, evidence that Stevens co-authored 

articles that contradict the disclosure of the ’291 patent 

specification does not alone establish that Stevens withheld those studies intending to deceive the PTO. 

We also disagree with the inference the district court 

drew from Stevens’s publication of the withheld data. 
CANCER RESEARCH v. BARR LABS 18

While publication to the scientific community is not the 

same as disclosure to the PTO and does not foreclose a 

finding of deceptive intent, see Bristol-Myers Squibb Co. v. 

Rhone-Poulenc Rorer, Inc., 326 F.3d 1226, 1241 (Fed. Cir. 

2003), the prompt publication of data in multiple articles 

over the entire course of prosecution is inconsistent with 

finding that intent to deceive is the single most reasonable inference to draw from the evidence in this case, see

Research Corp. Techs., Inc. v. Microsoft Corp., 536 F.3d 

1247, 1252 (Fed. Cir. 2008) (stating that “[p]ublication [to 

the scientific community] is an act inconsistent with an 

intent to conceal data from the USPTO.”). Also, Stevens 

did not selectively withhold information; the withheld 

information includes both positive and negative data 

regarding the claimed tetrazine derivatives. Cf. Semiconductor Energy Lab. Co. v. Samsung Elecs. Co., 204 F.3d 

1368, 1376 (Fed. Cir. 2000) (affirming a finding of intent 

to deceive based on a partial translation of a prior art 

reference). Accordingly, an equally reasonable inference 

to draw from the evidence is that Stevens viewed publication of all the data as important to his career as a scientist but did not appreciate their potential importance to 

the patentability of the tetrazine derivatives patent 

claims. 

Because we conclude that the district court committed 

clear error in finding that Stevens acted with deceptive 

intent, we need not address Cancer Research’s argument 

that the district court also erred in finding the withheld 

data highly material, and we reverse the district court’s 

decision holding the ’291 patent unenforceable for inequitable conduct. 
19 CANCER RESEARCH v. BARR LABS

CONCLUSION

For the foregoing reasons, we reverse the district 

court’s decision holding the ’291 patent unenforceable for 

prosecution laches and inequitable conduct. 

REVERSED 
United States Court of Appeals 

for the Federal Circuit 

__________________________ 

CANCER RESEARCH TECHNOLOGY LIMITED 

AND SCHERING CORPORATION, 

Plaintiffs-Appellants, 

v. 

BARR LABORATORIES, INC. AND

BARR PHARMACEUTICALS, INC., 

Defendants-Appellees. 

__________________________ 

2010-1204 

__________________________ 

Appeal from the United States District for the District 

of Delaware in case no. 07-CV-0457. 

__________________________ 

PROST, Circuit Judge, dissenting. 

I respectfully dissent. In my view, the majority opinion seriously errs in reversing the district court’s findings 

and conclusions that U.S. Patent No. 5,260,291 (“’291 

patent”) is unenforceable on the grounds of both prosecution laches and inequitable conduct. In doing so, the 

majority propounds a new and unsupportable legal standard for prosecution laches. With regard to inequitable 

conduct, the majority not only creates a new evidentiary 

standard, but it also ignores virtually unassailable credibility findings made by the district court after a four-day 

bench trial. I address each in turn below. 
CANCER RESEARCH v. BARR LABS 2

I. Prosecution Laches

The majority appears to not take issue with the district court’s findings and conclusion that the patentee’s 

almost decade-long delay in prosecuting its application—

caused by filing eleven continuation applications, abandoning ten of those applications, and obtaining nearly two 

years’ worth of time extensions merely to file continuation 

applications rather than responses to the Office Actions—

was unreasonable. Despite Cancer Research Technology 

Limited and Schering Corporation’s (collectively, “Cancer 

Research”) excuses justifying the delay, the information 

eventually used to overcome the examiner’s initial rejection was contained in the application as originally filed 

ten years earlier. The district court carefully rejected all 

of the patentee’s excuses for its delay, ultimately concluding that the applicants did not prosecute the application 

until it became commercially advantageous to do so. 

Instead, the majority rejects the legal standard the 

district court applied. The district court concluded that 

under Symbol Technologies, Inc. v. Lemelson Medical, 422 

F.3d 1378 (Fed. Cir. 2005) (“Symbol Techs. II”), prosecution laches does not require a showing of intervening 

rights, but rather turns on whether under the totality of 

the circumstances Cancer Research’s delay was unreasonable and unexplained. See Cancer Research Tech. v. 

Barr Labs., Inc., 679 F. Supp. 2d 560, 572-73 (D. Del. 

2010). Besides rejecting this standard, the majority says 

that in order to establish prosecution laches (1) prejudice 

to the alleged infringer must be shown, and (2) that 

prejudice requires that “either the accused infringer or 

others invested in, worked on, or used the claimed technology during the period of delay.” Maj. Op. at 9 (emphasis added); see also id. at 13-14 (“Barr has failed to 

establish either that it or that others developed or in-
3 CANCER RESEARCH v. BARR LABS

vested in temozolomide or any other claimed tetrazine 

compound between 1982 and 1991, the period of delay. 

Accordingly, Barr cannot establish prosecution laches as a 

matter of law . . . .”). 

First, I think the district court got it right because I 

do not agree with the majority that a showing of intervening rights, i.e. prejudice, is compelled by our precedent. 

Moreover, even if one could construe the case law as 

requiring prejudice, there is no basis, in the relevant case 

law or otherwise, for the majority’s further temporal 

limitation that the prejudice exists during the period of 

delay. 

Shifting the inquiry regarding prosecution laches 

from Cancer Research’s own conduct to the conduct of the 

party invoking the defense ignores that prosecution 

laches is an equitable defense. Neither the Supreme 

Court nor this court has required a defendant to establish 

prejudice to assert prosecution laches. Indeed, in Woodbridge v. United States, the Court held that a plaintiff’s 

willful or negligent postponement in obtaining patent 

rights alone can result in forfeiture. 263 U.S. 50, 57 

(1923) (quoting Kendall v. Winsor, 62 U.S. 322, 329 

(1858), for the proposition that an inventor “‘may forfeit 

his rights as an inventor by a willful or negligent postponement of his claims, or by an attempt to withhold the 

benefit of his improvement from the public until a similar 

or the same improvement should have been made and 

introduced by others’” (emphasis added)).1 Our precedent 

 1 The majority also cites to Webster Electric Co. v. 

Splitdorf Electic Co., 264 U.S. 463 (1924), Crown Cork & 

Seal Co. v. Ferdinand Gutmann Co., 304 U.S. 159 (1938), 

and General Talking Pictures Corp. v. Western Electric 

Co., 304 U.S. 175 (1938). None of these Supreme Court 

cases require a showing of prejudice where an applicant 
CANCER RESEARCH v. BARR LABS 4

is no more restrictive. Recognizing that prosecution 

laches is an equitable doctrine, we have declined to “set 

forth any firm guidelines for determining when such 

laches exists.” Symbol Techs. II, 422 F.3d at 1385. Laches may be triggered by “the totality of the circumstances, including the prosecution history of all of a series 

of related patents and overall delay in issuing claims.” Id.

at 1386. And we have specifically indicated that “repetitive refilings that demonstrate a pattern of unjustifiably 

delayed prosecution” “for the business purpose of delaying 

. . . issuance [of the patent]”—an apt description of Cancer 

Research’s behavior during the prosecution of the ’291 

patent—supports a finding of laches. Id. at 1385-86. 

 

unreasonably extends prosecution by refusing to respond 

to the merits of nine substantially similar Office Actions. 

Under Webster, “laches, equitable estoppel or intervening 

private or public rights” can each alone bar the right to a 

claim presented in a subsequent divisional patent. 264 

U.S. at 471 (emphasis added). The Webster Court suggested that there is a presumption that such claims are 

unreasonable (and thus time-barred) where the applicant 

waited more than two years to present the claims in a 

divisional application. Id. Under Webster, applicants 

could only obtain such claims if they provided justification 

for the more than two-year delay. Id. In Crown Cork, the 

Court clarified that “in the absence of intervening rights, 

the decision in [Webster] does not mean that an excuse 

must be shown for a lapse of more than two years in 

presenting the divisional.” 304 U.S. at 167-68; see also

General Talking Pictures, 304 U.S. at 184. Crown Cork

and General Talking Pictures make clear that a two-year 

delay in filing a divisional is not per se unreasonable in 

the absence of intervening rights. However, nothing in 

these cases requires a party to show that it had intervening rights or suffered any other prejudice as a prerequisite to asserting the equitable defense of prosecution 

laches where the patentee’s prosecution delays are unreasonable under the totality of the circumstances. 
5 CANCER RESEARCH v. BARR LABS

More importantly, even if prejudice is required, there 

is no basis for the majority’s new requirement that one 

must confine himself to the period of prosecution delay in 

determining whether prejudice exists. Such a requirement (1) discounts the relationship between prosecution 

laches and broad public interests in the timely issuance of 

patents and (2) imposes a novel time restriction on the 

harm suffered. 

By requiring this particularized prejudice, the majority sidesteps the real harm at issue in this case. The 

Supreme Court has explicitly recognized that delaying a 

patentee’s monopoly period harms the public by delaying 

its free use of the patented invention. Woodbridge, 263 

U.S. at 48-49. Here, the applicant first filed the patent 

application disclosing temozolomide in 1982. By stalling 

prosecution for its own business purposes for nearly a 

decade, Cancer Research obtained a patent which does 

not expire until 2014—almost thirty-two years after the 

first application in this chain was filed. The majority 

downplays the public prejudice caused by this delay,2

Maj. Op. at 12-13; however, Cancer Research’s conduct 

has prejudiced the public by extending its patent monopoly over temozolomide. Indeed, Congress has specifically 

recognized the public’s interest in obtaining affordable 

prescription drugs by enacting a regulatory scheme to 

expedite the availability of generic drugs. See Drug Price 

Competition and Patent Term Restoration Act of 1984, 

Pub. L. No. 98-417, 1984 Stat. 1538 (codified as amended 

 2 While the majority suggests Cancer Research itself “incurred a cost” due to the prosecution delay, that 

Cancer Research’s delay resulted in its not getting the full 

patent term extension has absolutely no relevance to 

whether public or private interests were prejudiced by the 

delay. 
CANCER RESEARCH v. BARR LABS 6

in scattered sections of 21 & 35 U.S.C.). Barr Laboratories, Inc. and Barr Pharmaceuticals, Inc. (collectively, 

“Barr”), as well as other makers of generic pharmaceuticals, are likewise harmed. It is unable to enter the market without risking a patent infringement suit until a 

date far later than the one it would have faced had Cancer Research not engaged in its excessive delays. 

The majority avoids entirely these harms by confining 

the relevant harm to the period during which Cancer 

Research delayed prosecution of its patent application. 

There is no basis for the majority’s limitations. I would 

hold that the more generalized harm associated with the 

improper extension of the patent monopoly, including the 

accompanying market uncertainty and denial to the 

public of free use of the invention, is sufficient prejudice 

to justify the use of an equitable defense. Even if our 

precedent required adverse intervening rights, it is not 

appropriate to confine the inquiry to the period of time 

when Cancer Research was actively delaying prosecution. 

The harm continued though the patent term “extension” 

Cancer Research improperly created though its delay 

tactics. 

II. Inequitable Conduct 

Similarly, in reversing the district court’s findings 

and conclusions regarding inequitable conduct, the majority veers from our precedent in at least two respects: (1) 

it creates a new evidentiary standard for establishing 

inequitable conduct, and (2) it inexplicably rejects the 

district court’s unassailable credibility determinations, 

which served as the basis for its conclusion that inequitable conduct occurred. 
7 CANCER RESEARCH v. BARR LABS

Again, in my view, the district court got it exactly 

right. Here, an inventor, Dr. Stevens, withheld important 

data from the U.S. Patent and Trademark Office (“PTO”) 

that contradicted the disclosure in the patent applications. The majority does not take issue with the district 

court’s conclusion that this data was highly material. 

Clearly, it could not, because at a minimum the disclosure 

would have affected the scope of the patent granted. 

Rather, it rejects the district court’s credibility determination that Dr. Stevens’s explanation for not submitting this 

highly material data was belied by the facts that Stevens 

found the data conclusive enough (and sufficiently nonconfidential) to publish the data and his conclusions of 

inactivity or toxicity to the scientific community. Stevens 

did not qualify his statements regarding inactivity. 

Certainly, if Stevens found the information sufficiently 

accurate to base conclusions upon and to publish to his 

peers, it was sufficiently accurate and conclusive enough 

to submit to the PTO. Cancer Research, 679 F. Supp. 2d 

at 581. 

The majority’s rejection of the findings and conclusions of the trial judge rests on two faulty pillars. The 

majority first missteps by determining that materiality 

and intent require separate evidentiary bases. The 

majority concludes that the district court erred because it 

“did not rely on any other evidence to support its finding 

of deceptive intent beyond that used to find the withheld 

data material.” Maj. Op. at 17. Requiring separate 

evidence for each prong, however, has no basis in our 

precedent. The majority is correct that the district court 

cited to the same evidence in support of its findings of 

intent and materiality. But it by no means rested on its 

finding of materiality to infer intent. Rather, the evidence presented at trial separately supports the district 

court’s findings on both prongs, and when combined with 
CANCER RESEARCH v. BARR LABS 8

the district court’s credibility findings regarding Dr. 

Stevens’s “explanation” for his failure to disclose, is 

absolutely sufficient to support the conclusion that highly 

material evidence was withheld from the PTO with intent 

to deceive. 

Further, the majority’s treatment of the district 

court’s credibility determinations—which are virtually 

unreviewable by this court—is baffling. See LNP Eng’g 

Plastics, Inc. v. Miller Waste Mills, Inc., 275 F.3d 1347, 

1361 (Fed. Cir. 2001). The majority concludes that the 

district court did not draw the most reasonable inference 

regarding Stevens’s withholding of the published data. 

Maj. Op. at 17-18. Instead, the majority believes that 

there is another “an equally reasonable inference”—

Stevens did not appreciate the potential importance of the 

data to the patentability of the claims. We should not 

draw inferences that the district court has already excluded based on its own credibility findings with respect 

to Stevens’s explanations for the withholding. 

In sum, in light of our prosecution laches precedent, I 

would not require that Barr have intervening rights 

during the period that Cancer Research delayed prosecution of its patent. Even if I did, I would not limit the 

prejudice inquiry to the period of delay. Further, given 

our differential standard of review, I cannot agree that 

the district court’s intent finding with regard to inequitable conduct is clearly erroneous. Accordingly, I would 

uphold the district court’s application of prosecution 

laches and its finding of inequitable conduct.