Assignor Estoppel Precluded by AIA Statutes…But What of Other Equitable Defenses?

The doctrine of assignor estoppel bars the assignor of a patent from challenging the validity of the patent after it is assigned. In considering this defense to an AIA trial proceeding, the Patent Trial & Appeal Board (PTAB) had consistently held that this common-law doctrine is subject to abrogation by statute, and that the AIA statutes do exactly that. The Federal Circuit recently agreed.

However, the Board has considered and applied other equitable defenses. For example, the Board has applied waiver (prior to the Federal Circuit’s determination that tribal immunity did not apply to the PTAB). Thus, equitable defenses that do not conflict with the AIA statutes may be leveraged.

One equitable defense that could become more prominent going forward —given the alignment of claim construction standards between the PTAB and courts— is judicial estoppel.


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