Immunizing Patent Portfolios Against “Infectious” Estoppel

by Perkins Coie

Parties challenging patents under the post-issuance review proceedings authorized by the America Invents Act have long worried about estoppel in later district court cases if they lose before the Patent Trial and Appeal Board (PTAB).  Challengers should not be alone in their fears, however.  Now that the Patent and Trademark Office (PTO) has adopted broad estoppel rules for patent owners, patent owners also face significant risks of estoppel in pending or future proceedings before the PTO. 

Although post-issuance proceedings usually target only one or a few patents, the new estoppel provisions allow a canceled claim or denied amendment to “infect” other patents in the same patent family.  As a result, patent owners not only risk losing the claims at issue before the PTAB, they may also be barred from arguing the validity of claims in other patents where the PTO deems those claims “patentably indistinct.”  Given this risk, patent owners should take a proactive strategy in developing their patent portfolios that minimizes the vulnerability of an entire patent family based on a challenge to one or a few of the patents within that family.

What Is Patent Owner Estoppel?

Under the new rules, when a patent claim is canceled or an amendment is denied during a post-issuance proceeding before the PTAB, the patent owner is precluded from taking action inconsistent with that adverse judgment.  See 37 C.F.R. § 42.73(d)(3).  In particular, § 42.73(d)(3) creates an estoppel barring any claim in any patent that is patentably indistinct from a claim that was canceled or refused during a PTAB proceeding.  A patent claim is patentably indistinct from a canceled or refused claim if it has the same scope as the canceled or refused claim or is merely an obvious variant of the canceled or refused claim.

The estoppel could potentially apply both to issued patents subjected to post-grant proceedings and having the same specification, and to pending applications with the same specification (continuation applications).  The estoppel may also apply to patents that do not have the same specification and the same priority date.   

By rule, an unsuccessful patent owner has a duty to disclose any adverse decisions in related pending applications and subsequent proceedings before the PTO.  Furthermore, under 35 U.S.C. § 122(e), successful challengers can ensure that examiners of related pending applications based on the same specification are aware that the challenge succeeded, although the relatively strict time constraints of § 122(e) may limit the usefulness of this procedure.   

Strategies to Minimize the Potential Effects of Patent Owner Estoppel

Patent owner estoppel is particularly significant to patentees who invest in and maintain large patent portfolios.  Continuation practice remains a common strategy for patent owners to refine portfolios to hinder potential infringers’ attempts to design around earlier issued claims.  Filing related, follow-up applications and patents directed to invention updates is also a common tactic to stay ahead of competitors.  So what can patent owners do to minimize the effect of patent owner estoppel? 

(I) Maintain a Pending Application

Even though continuation applications are the most likely targets of patent owner estoppel, the filing of one or more continuing pending applications during the enforceable term of a patent still gives the patent owner more strategic flexibility, both defensively and offensively.  Offensively, a patent owner may seek to present claims in continuation applications that read on new developments from competitors.  Defensively, a patent owner may submit newly discovered prior art and adapt to new challenges to the claims in a pending application. 

Patent owners may also consider requesting accelerated examination of pending applications when a challenge is asserted against a related patent.  In the accelerated examination, the patent owner may address any vulnerabilities exposed by the challenge.  The patent owner may also be able to obtain an on-record agreement with the examiner that the new claims are patentably distinct from the challenged claims.  Finally, the patent owner may race to obtain another patent before any final judgment in the proceeding challenging the issued patent and thereby avoid the threat of patent owner estoppel.

(II) Restriction Practice as a Shield From Patent Owner Estoppel

Although in most cases it will remain advantageous to maintain continuation applications, patent owners can tactically encourage more restriction requirements and divisional applications to shield themselves from patent owner estoppel.  Because the PTO presumes that claims in divisional applications are patentably distinct, encouraging restriction practice may be an effective way of insulating claims from future patent owner estoppel. 

To issue a restriction requirement, an examiner must find that the claimed inventions subject to the requirement are “independent” or “distinct.”  Independent inventions are unrelated with no clear relationship between them.  Inventions are distinct when they are related but are (1) capable of separate manufacture, use or sale and (2) where at least one of the inventions is patentable over the other.  For example, claims that represent different statutory classifications (i.e., a product and the process of making a product) are commonly found to be distinct.  Examiners often require restriction between multiple claimed inventions in a single application when the inventions have separate classifications or separate status in the art or require different fields of search.

With these rules in mind, patent applicants can strive to provoke a restriction requirement by filing within initial applications all claims directed to different statutory subject matters (e.g., product and process claims), different classifications, and/or different fields of search.  It should be understood, however, that the need to file divisional applications incurs additional and potentially burdensome costs, especially when a multiway restriction is imposed.  Thus, a patent owner needs to balance the costs and potential benefits when accepting or traversing a restriction requirement. 

(III) Caution in Using Terminal Disclaimers

Terminal disclaimers are commonly used to overcome obviousness-type double patenting rejections over commonly owned patent claims.  But such a strategy is potentially dangerous if the claims over which new claims have been rejected are canceled or refused in a proceeding before the PTAB.  Patent owners may want to be cautious about using terminal disclaimers and should consider trying to overcome obviousness-type double patenting rejections by argument and/or claim amendments.

(IV) Make It More Difficult for Potential Challengers

(A) Present More Claims of Varying Scope

It is more difficult and more costly for challengers to address multiple claims with overlapping scopes.  Adding dependent claims can also provide varying scopes of protection, which are more likely to be “patentably distinct.”  A patent owner can also vary the terms used in different claims to provide flexibility both in asserting patentable distinctness and in avoiding newly discovered prior art. 

(B) Enhance Portfolio Diversity with Multiple Related but Distinct Patent Families

As an alternative to provoking restriction practice, it may make sense in certain situations to divide related inventions into related but distinct patent families instead of including all related inventions in a single application.  Although a patent owner may use different terms in different claims of the same patent, or in patents of the same patent family, different terms used in different patent families are more likely to be construed differently.  Adopting such a strategy allows the patent applicant more flexibility to choose different terminologies in the related but distinct patent families and to capture different patentable aspects of the invention, while providing additional rationales for arguing that inventions are patentably distinct. 

In pursuing this strategy, it is likely to be most advantageous to file the applications in the different patent families on the same date to avoid creating potential prior art issues between the patent families.  The timing and coordination of filing in this way may be impractical, however.  In addition, there will be a substantial cost and management burden to maintain consistent prosecution over multiple patent families at the same time.   


Patent owners may consider using the strategies described above to minimize the effect of patent owner estoppel and to limit the scope of potential patent challenges.  However, the proposed strategies often come with additional costs that may outweigh their benefit.  Keeping a pending application is highly recommended to maintain claim drafting flexibility, which may prove important in addressing the effect of any patent owner estoppel.  Provoking restriction requirements is also recommended, as long as the cost to accept such restriction is reasonable.

DISCLAIMER: Because of the generality of this update, the information provided herein may not be applicable in all situations and should not be acted upon without specific legal advice based on particular situations.

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