Key Takeaways

  • IPR estoppel prevents parties from reusing arguments in litigation that they reasonably could have raised in an inter partes review (IPR).
  • Courts have debated whether estoppel applies only to arguments actually raised, or also to those that could have been raised but were not.
  • The America Invents Act (AIA) made estoppel mandatory, creating ongoing disputes about its scope and application in district courts.
  • The Federal Circuit has clarified that estoppel applies broadly to prior art references that a skilled searcher could have located and presented during the IPR.
  • Recent developments limit estoppel’s reach in some contexts, such as with system art (evidence of actual devices or systems), which the PTAB often cannot evaluate, leaving such defenses available in litigation.
  • Strategic considerations for patent challengers include whether to file an IPR at all, how broadly to draft petitions, and anticipating potential estoppel effects.

The IPR estoppel rule puts certain restrictions on a petitioner's ability to challenge a patent.

Current IPR Estoppel Rules

The purpose of the inter partes (IPR) estoppel rule is to prevent frivolous challenges to patents before the United States Patent and Trademark Office's (USPTO) Patent Trial and Appeal Board (PTAB). Under this rule, challenges to patents cannot be based on grounds that could have been raised during an IPR.

Typically, common law estoppel rules can be different depending on the jurisdiction, and in most cases, will be left up to the discretion of the court. Under 35 U.S.C. Section 315(e), however, estoppel is mandatory. Generally, when an IPR is requested, the petitioner will have a variety of grounds for contesting the patent.

The PTAB will accept or decline requests for an inter partes review on an individual basis and will have several options for responding to the request:

  • Declining to institute the IPR.
  • Allowing the IPR to proceed on all grounds.
  • Accepting the IPR on certain grounds.

There will be two stages to an IPR: discovery and hearing. After these stages have been completed, a final decision will be issued by the PTAB. Estoppel rules will apply both to proceedings of the PTAB and district courts. Multiple grounds can result in an IPR estoppel. Recently, the PTAB and the courts have developed different understandings of the estoppel rules in Section 315(e), including the scope of these rules and how they can be applied.

Key Federal Circuit Clarifications

The Federal Circuit has repeatedly emphasized that IPR estoppel applies to any prior art reference that a skilled searcher, using reasonable diligence, could have found before the petition was filed. This broad interpretation prevents petitioners from strategically withholding references to use later in district court litigation. For example, in California Institute of Technology v. Broadcom Ltd., the court confirmed that estoppel reaches both prior art patents and printed publications that “reasonably could have been raised” during the IPR. This expansive view ensures that IPR remains a final, comprehensive forum for validity challenges.

Grounds for IPR Estoppel

A variety of court cases are related to whether or not estoppel applies to an inter partes review. In one case, for instance, the court ruled that estoppel rules will not apply until the IPR has actually been instituted by the PTAB. This is because non-instituted grounds could not have been raised because the IPR never actually took place.

In another case, it was decided that simply because an IPR contention was denied, it doesn't mean that the contention is invalid. The court in this case also reasoned that grounds that have not been instituted do not mean that estoppel is applicable.

Limits on Estoppel in Practice

Despite the broad statutory language, estoppel is not absolute. District courts have recognized circumstances where estoppel does not apply, such as:

  • Non-instituted grounds: If the PTAB declines to institute review on certain grounds, courts have generally ruled that estoppel does not apply to those grounds in later litigation.
  • System art and non-patent literature: Because the PTAB is limited to evaluating patents and printed publications, challengers may still rely on evidence of physical systems, prior uses, or other real-world practices in litigation without being estopped.
  • Newly discovered references: If a challenger can demonstrate that certain references were not discoverable with reasonable diligence before the petition, courts may permit their use despite estoppel restrictions.

These exceptions demonstrate that while estoppel is powerful, it has boundaries shaped by practical limits on what an IPR can address.

The Changing Scope of Estoppel

One of the most important pieces of legislation related to estoppel is the America Invents Act of 2011. This act changed the rules for challenging a patent that had already been granted. Basically, the AIA states that a person challenging a patent by requesting an IPR cannot assert that the patent is invalid based on grounds that would have been reasonably raised during the IPR.

While this may seem fairly straightforward, district courts have had a very difficult time determining the actual scope of the IPR estoppel rules. The two factors that have complicated this issue are grounds that the USPTO did not institute but were included in the petition, and grounds that should have been known but were not included in the petition.

One recent case in the United States District Court in Massachusetts went against traditional understanding by not applying estoppel rules for either of these grounds. The court ruled in this manner because it was reluctant to broaden the current estoppel rules. District courts have increasingly come to the opinion that estoppel does not apply to grounds that were included in the petition but were not instituted by the PTAB. Estoppel does apply, however, to grounds that the petitioner should have raised but failed to do so.

This decision made by the Massachusetts District Court represents a big change in how the scope of estoppel rules are viewed. This new view restricts estoppel from being applied to grounds that were not included in an inter partes review.

A pending Supreme Court decision may have a big impact on IPR estoppel, although the question being raised is different than the previously mentioned district court cases. The question in front of the court is whether the PTO is required to institute an IPR on all the challenged claims of a patent or if it has the ability to pick and choose which claims will be reviewed. Depending on the final ruling of the court, the scope of IPR estoppel rules, as well as how these reviews take place, may be greatly altered.

Strategic Implications for Patent Litigants

Because of its evolving scope, IPR estoppel is now a central consideration in patent litigation strategy. Petitioners must weigh:

  1. The risk of losing defenses: A failed IPR may foreclose large portions of prior art defenses in district court.
  2. Petition drafting: Overly broad petitions may increase the chance that useful grounds are estopped, while narrowly tailored ones risk missing important challenges.
  3. Timing: Filing an IPR early may preserve litigation flexibility, but it may also accelerate estoppel effects if the PTAB issues a decision before trial.
  4. Settlement leverage: Knowing that estoppel may cut off defenses can influence negotiations between patent owners and challengers.

Ultimately, petitioners must approach IPR estoppel as both a risk and a tool: it can streamline disputes but also limit litigation defenses if not carefully managed.

Frequently Asked Questions

1. What is IPR estoppel?

IPR estoppel prevents a party from raising in litigation any invalidity arguments that were or reasonably could have been raised during an inter partes review.

2. Does estoppel apply to grounds the PTAB did not institute?

Generally, no. Courts have held that estoppel does not apply to grounds explicitly denied institution by the PTAB.

3. Can I use system art in litigation after an IPR?

Yes. Because the PTAB cannot evaluate system art, courts have allowed litigants to rely on such evidence even after losing an IPR.

4. How has the Federal Circuit clarified estoppel?

The court has held that estoppel extends to all prior art references that a diligent searcher could have found, not just those actually raised.

5. How should companies consider estoppel when filing IPRs?

They should balance the benefits of early validity challenges against the risk of losing defenses in litigation, carefully drafting petitions to preserve strategic flexibility.

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