NOTE: This disposition is nonprecedential.

United States Court of Appeals 

for the Federal Circuit ______________________ 

IGT,

Plaintiff/Counterclaim Defendant-Appellant

v.

ARISTOCRAT TECHNOLOGIES, INC.,

Defendant/Counterclaimant-Appellee

ARISTOCRAT TECHNOLOGIES AUSTRALIA PTY 

LIMITED, ARISTOCRAT INTERNATIONAL PTY. 

LTD.,

Counterclaimants-Appellees

______________________ 

2015-2083

______________________ 

Appeal from the United States District Court for the 

District of Nevada in No. 2:15-cv-00473-GMN-GWF, 

Judge Gloria M. Navarro.

______________________ 

Decided: May 12, 2016

______________________ 

 ADAM MORTARA, Bartlit Beck Herman Palenchar &

Scott LLP, Chicago, IL, argued for plaintiff/counterclaim 

defendant-appellant. Also represented by REID M.

BOLTON, JASON LLOYD PELTZ, BRIAN SWANSON; DANIEL 

CHARLES TAYLOR, Denver, CO.
2 IGT v. ARISTOCRAT TECHNOLOGIES, INC. 

 ROBERT T. HASLAM, Covington & Burling LLP, Redwood Shores, CA, argued for defendant/counterclaimantappellee and counterclaimants-appellees. Also represented by AUSTIN KEILLER HAMPTON, GARY RUBMAN, PETER 

ANDREW SWANSON, Washington, DC.

______________________ 

Before PROST, Chief Judge, NEWMAN and LOURIE, Circuit 

Judges.

PROST, Chief Judge. 

IGT appeals the district court’s denial of its motion for 

a preliminary injunction to prohibit Aristocrat from 

challenging the validity of IGT’s patents at the U.S. 

Patent and Trademark Office (“PTO”). IGT argues that 

the doctrine of assignor estoppel precludes invalidity 

challenges by Aristocrat, and that IGT would suffer 

irreparable harm if Aristocrat were to file a petition for 

inter partes review and succeed in cancelling IGT’s patent 

claims. The district court denied IGT’s motion. IGT v. 

Aristocrat Techs., Inc., No. 2:15-cv-473 (D. Nev. Sept. 18, 

2015) (“District Court Decision”). While we agree with the 

district court that the circumstances existing at the time 

of its decision were too speculative to justify a preliminary 

injunction, we vacate and remand for the court to consider 

recent updates in events. 

I 

This suit began in March of 2015, when IGT filed a 

complaint alleging that Aristocrat’s slot machines infringed ten of IGT’s patents. In July of 2015, IGT moved 

to preliminarily enjoin Aristocrat from challenging the 

validity of four of IGT’s patents at the PTO on the basis of 

assignor estoppel. IGT alleged that Joseph Kaminkow, 

the named inventor on the four patents, worked for IGT 

from 1999 to 2012; that he assigned these patents to IGT 

during his employment there; that he later joined Aristo-
IGT v. ARISTOCRAT TECHNOLOGIES, INC. 3

crat in 2013; and that he was involved in Aristocrat’s 

development of the accused slot machines. IGT argued 

that Mr. Kaminkow, having assigned the patents for 

value, was precluded from challenging their validity 

under the doctrine of assignor estoppel. Diamond Scientific Co. v. Ambico, Inc., 848 F.2d 1220, 1224 (Fed. Cir. 

1988) (“Assignor estoppel is an equitable doctrine that 

prevents one who has assigned the rights to a patent (or 

patent application) from later contending that what was 

assigned is a nullity.”). And IGT argued that Aristocrat 

was precluded from doing so as well, as assignor estoppel 

applies not only to the assignor himself, but also to other 

parties in privity with the assignor when the assignor 

bears a sufficiently close relationship to the party’s infringing activity. See Intel Corp. v. U.S. Int’l Trade 

Comm’n, 946 F.2d 821, 839 (Fed. Cir. 1991) (“What is 

significant is whether the ultimate infringer availed itself 

of the inventor’s ‘knowledge and assistance’ to conduct 

infringement.” (citations omitted)).

To satisfy the four-factor preliminary injunction test, 

IGT argued that: (1) IGT was likely to succeed in establishing applicability of the assignor estoppel doctrine; (2) 

IGT would suffer irreparable harm if Aristocrat were to 

file a petition for inter partes review and succeed in 

cancelling IGT’s claims; (3) the balance of equities favored 

IGT; and (4) enjoining Aristocrat from filing a petition for 

inter partes review served the public interest. 

The district court denied IGT’s motion for failure to 

establish the second factor, likelihood of irreparable 

harm. The court explained:

Multiple contingencies must occur before Defendant’s petition would injure Plaintiff. Specifically, 

the United States Patent Office would have to institute the proceedings and reach a finding of invalidity before Plaintiff would actually suffer injuries 

from Defendant’s petition. Since, at this time, the 
4 IGT v. ARISTOCRAT TECHNOLOGIES, INC. 

Court cannot predict whether the Patent Office will 

decide to institute inter partes review, the circumstances Plaintiff offers show a possibility of injury, 

but are too contingent to satisfy the likelihood of 

irreparable harm standard.

District Court Decision at 7. In addition to finding a lack 

of a likelihood of irreparable harm, the court also noted 

that inter partes review is “a statutorily permitted procedure” and that Aristocrat “would not infringe on any of 

[IGT’s] legal rights by pursuing such action.” Id. at 7-8. 

We have jurisdiction pursuant to 28 U.S.C. 

§§ 1292(c)(1) and 1295(a)(1). We review a denial of preliminary injunction for abuse of discretion. Takeda 

Pharm. U.S.A., Inc. v. W.-Ward Pharm. Corp., 785 F.3d 

625, 629 (Fed. Cir. 2015).

II

IGT’s request for a preliminary injunction is premised 

on its observation that the PTO does not recognize assignor estoppel as a defense in inter partes review or 

reexamination proceedings.1 Given this state of affairs, 

IGT argues that a preliminary injunction is its best 

recourse to prevent Aristocrat, a party whom it argues is 

estopped from challenging validity in the district court, 

from making an end-run around the doctrine by invalidating IGT’s patents at the PTO instead. 

 

1 See Redline Detection, LLC v. Start Environtech, 

Inc., No. IPR2013-00106, 2013 WL 5970197, at *2 

(P.T.A.B. Aug. 27, 2013) (refusing to apply assignor 

estoppel in inter partes review proceeding); Inter partes

reexamination No. 95/000,120, at 12-14 (July 19, 2006) 

(refusing to apply assignor estoppel in inter partes reexamination proceeding). 
IGT v. ARISTOCRAT TECHNOLOGIES, INC. 5

We begin by clarifying what we are not deciding in 

this case. Although both parties brief the question of 

whether or not the doctrine of assignor estoppel should

apply in PTO proceedings, they both conclude that we 

need not answer that question in this case. We agree. 

That question is not properly before us and we therefore 

render no opinion on it.2 Rather, we address in this case 

only the narrow question that has been appealed: whether or not the district court was correct in denying IGT’s 

motion for preliminary injunction.

We answer that question in the affirmative. A movant seeking a preliminary injunction must show that 

“irreparable injury is likely in the absence of an injunction.” Winter v. Natural Res. Def. Council, Inc., 555 U.S. 

7, 22 (2008). It is not enough to show a “possibility” of 

harm, as “a possibility of irreparable harm is inconsistent 

with [the] characterization of injunctive relief as an 

extraordinary remedy that may only be awarded upon a 

clear showing that plaintiff is entitled to such relief.” Id.

Here, the district court was correct that IGT failed to 

show a likelihood of irreparable harm. At the time IGT 

filed its motion, Aristocrat had not even filed petitions 

seeking inter partes review. There were therefore multiple events yet to occur before IGT would potentially 

experience cancellation of its claims: Aristocrat would 

need to file a petition seeking inter partes review; the 

PTO would need to conclude that there was a reasonable 

likelihood that Aristocrat would prevail in its invalidity 

challenge and actually institute inter partes review 

proceedings; the PTO would need to conduct an adminis-

 

2 Accordingly, we express no opinion on the district 

court’s comment that, “[b]ecause inter partes review is a 

statutorily permitted procedure, Defendant would not 

infringe on any of Plaintiff’s legal rights by pursuing such 

action.” District Court Decision at 7-8. 
6 IGT v. ARISTOCRAT TECHNOLOGIES, INC. 

trative trial to evaluate the merits of Aristocrat’s position; 

and, ultimately, the PTO would need to conclude that 

Aristocrat had succeeded in proving IGT’s claims invalid. 

As the district court correctly noted, these circumstances 

are far “too contingent to satisfy the likelihood of irreparable harm standard.” District Court Decision at 7. 

Since the district court’s decision, however, Aristocrat 

has filed petitions seeking inter partes review on all four 

of IGT’s patents, and the PTO has thus far instituted two 

of the four. While IGT asks us to consider these changed 

circumstances in evaluating the propriety of a preliminary injunction, we decline to do so. It is up to the district 

court, in the first instance, to determine whether and how 

the filing and institution of Aristocrat’s petitions weigh in 

the preliminary injunction analysis. The proper course of 

action, therefore, is to vacate and remand to allow the 

parties to argue the impact of the changed circumstances 

to the district court.

For the reasons expressed herein, we vacate and 

remand. 

VACATED AND REMANDED