Part 1 of this series focused on the importance of a good prior art search prior to filing a request for inter partes reexamination.  Part 2 examines the exceptions to the estoppel provisions of § 315(c).  Specifically, this blog entry identifies situations in which a party might still be able to contest in litigation the validity of a patent that was the target of an unsuccessful request for inter partes reexamination.

Estoppel does not apply to patent claims for which no request for reexamination was ordered.  Simply filing a request for inter partes reexamination, by itself, does not automatically trigger estoppel.  The language of § 315(c) does not trigger estoppel unless the “request for inter partes reexamination results in an order under section 313.”  For any request for which the Patent Office does not find a substantial new question of patentability, there is no estoppel.  Thus, estoppel still applies in situations where the Patent Office orders reexamination of a patent claim on the basis of some, but not all, of the prior art presented by the third-party requester as raising a substantial new question of patentability of that patent claim.

Estoppel only applies to the third-party requester.  The estoppel provision of § 315(c) applies not only to a “third-party requester” but also possibly those in privy with the third-party requester as a real party-in-interest.  The express language of § 315(c) is different from the estoppel provision of 35 U.S.C. § 317, which applies to third-party requesters and their privies with respect to subsequent requests for inter partes reexamination.  Thus, one might assume, that the § 315(c) estoppel applied to litigants is more limited than the § 317 estoppel applied to future requests for inter partes reexamination.  The problems with that assumption are exposed when one considers that a third-party requester acting for the benefit of a litigant is really placing the litigant in the position of the real party-in-interest.  Although § 315(c) literally applies only to the third-party requester, the provisions of § 315(c) could easily be subverted if the term “third-party requester” were limited to the particular attorney or entity making the request.  Thus, it is unlikely that a litigant can avoid estoppel if another entity makes a request for inter partes reexamination designed to benefit the litigant.  (See related blog post, discussing Troll Busters LLC.)  Practically speaking, courts should interpret “third-party requester” to include real parties-in-interest.

Another scenario that arises frequently is one in which there are multiple accused infringers in a litigation.  If some parties choose to participate in the filing of a request for inter partes reexamination while other parties opt out, do the parties opting out fall victim to the estoppel provision of § 315(c)?  In these situations, the parties should not be estopped from presenting any invalidity arguments in litigation merely because they made a strategic decision not to participate in inter partes reexamination.

Estoppel does not apply to invalidity grounds which the requester could not have raised in inter partes reexamination.  Because a request for inter partes reexamination can only be based on patents and printed publications, prior art that is neither a patent nor a printed publication is fair game in an invalidity defense in subsequent litigation proceedings.  This issue was analyzed in the case of ACCO Brands, Inc. v. PC Guardian Anti-Theft Products, Inc.  In that case, the court determined that “estoppel does not apply to grounds for invalidity based on prior art that was not and could not have been before the PTO.”  The plaintiff sought to prevent the defendant from using physical samples of computers as a basis for invalidity because the defendant had relied upon printed brochures for those computers as a basis for inter partes reexamination, which resulted in the confirmation of all claims of the plaintiff’s patent.  The court declined to invoke the estoppel provision of § 315(c) to prevent the defendant from relying on the physical computers as evidence of invalidity because the computers were not patents or printed publications – the only type of prior art that the Patent Office considers during reexamination – and they raised new issues with respect to the novelty of certain claim limitations.

Estoppel does not apply to prior art that was unavailable.  The language of § 315(c) prevents estoppel from operating with respect to “newly discovered prior art unavailable to the third-party requester and the Patent and Trademark Office at the time of the inter partes reexamination proceedings.”  This exception can be viewed as a specific statutory example of invalidity grounds that fall outside the “could have raised” language in § 315(c), but it is significant enough to warrant separate discussion.  Clearly, there is no estoppel under § 315(c) if a particular patent or printed publication did not exist at the time of the inter partes reexamination proceedings, and clearly there is estoppel if the third-party requester had actual knowledge of a particular patent or printed publication.  In between those extremes, there is little guidance from the case law as to what constitutes “unavailable” prior art.

The conference reports pertaining to § 315 appear to impose an actual knowledge requirement for prior art to be considered unavailable:  “Prior art was unavailable at the time of the inter partes reexamination if it was not known to the individuals who were involved in the reexamination proceeding on behalf of the third-party requester and the US Patent Office.”  H.R. Rep. No. 106-464 (November 9, 1999).  The Patent Office however, has taken a view that is less accommodating to third-party requesters. Under the Patent Office view, a court, depending on the particular facts and circumstances, can exclude prior art that could have been discovered through a diligent search for prior art. USPTO Report to Congress on Inter Partes Reexamination at 6; Official Gazette 1234:97 (May 23, 2000).

In practice, a court is more likely interpret the phrases “could have raised” and “unavailable” broadly to include prior art that could have been discovered through a diligent search.  Such a policy serves to conserve judicial resources by reducing the number of invalidity issues that can be raised in litigation and serves to provide a quid pro quo for an accused infringer seeking to stay litigation pending the results of inter partes reexamination.  If a third-party requester is permitted to deliberately remain ignorant of patents and printed publications that would otherwise be discovered through a diligent search, then there is less incentive for the court to grant a stay of litigation because inter partes reexamination could not eliminate from the litigation the patents and printed publications that the accused infringer uncovers at the conclusion of the inter partes reexamination proceedings.  Thus, as recommended in part 1 of this series, a third-party requester is well-advised to perform an exhaustive search for prior art prior to requesting inter partes reexamination or risk being estopped from relying on late-discovered prior art in litigation.

Estoppel does not apply until a claim is finally determined to be valid and patentable.  The statutory phrase “finally determined” is subject to interpretation because § 315(c) does not expressly state whether estoppel attaches when a final office action issues or when a certificate of reexamination issues, for example.  Because a final office action does not necessarily preclude a patent owner from amending claims, the practical application of the phrase “finally determined” will most likely mean when a certificate of reexamination issues, or after a notice of intent to issue a certificate of reexamination issues and all appeals have been exhausted.  See, e.g., Safoco, Inc. v. Cameron Int’l Corp., No. 05-0739 (S.D. Tex. July 31, 2009) (concluding that § 315(c) estoppel does not attach until the Office issues a reexamination certificate).  Thus, when patentability is not “finally determined,” a third-party requester may be able to present in a parallel litigation the same invalidity arguments that it has presented in a parallel inter partes reexamination proceeding.


The estoppel provision of § 315(c) should not, by itself, scare a party away from inter partes reexamination.  A party must give thorough consideration to all of the potential exceptions to estoppel and whether they apply in any particular situation.  Lastly, if an exhaustive search of prior has been performed, then inter partes reexamination proceedings should be viewed as an alternative to litigation for having issues of invalidity determined.