Estoppel from Inter Partes Review or Post Grant Review
A third party requester is estopped from subsequently arguing during a litigation that a claim is invalid based on grounds that were "raised or could have been raised" during the reexamination. As such, if the third party requestor was aware of a prior art publication during the inter partes reexamination, the requestor, and those in privy thereto, will be estopped from utilizing that prior art publication as part of an invalidity defense in a subsequent litigation even if the prior art was not presented during the reexamination.
This prohibition does not, however, prevent an accused infringer from requesting an Ex Parte Reexamination. In fact, the Federal Circuit has affirmed a PTO finding of invalidity in an Ex Parte Reexamination requested by a party whose assertion of invalidity, on the basis of the same prior art, had been rejected in court.
A challenger in either case may assert invalidity in the later proceeding based on newly discovered prior art unavailable during the earlier proceeding.
Prior to the AIA, the estoppel was specifically limited to "civil actions" in district court (e.g., it does not relate to ITC proceedings). Under AIA, the estoppel extends to ITC proceedings as well.