Terms and Concepts


Official PTO statistics indicate that 65% of ex parte and 43% of inter partes reexaminations result in some change to the claims. In 12% of ex parte and 49% of inter partes reexaminations, all claims are canceled outright.  Where claims are substantively amended, the accused infringers may not be liable for past damages under intervening rights law.  This can be crucial where the patent term is short or the accused infringers have clear and inexpensive design-around options.

More specifically, substantive amendments made during reexamination may defeat damages for past infringement under the statutory doctrine of intervening rights [35 U.S.C. §§ 252, 307(b), 316(b)].  A patent owner cannot seek damages for claims that are not substantially identical to the original claims [Bloom Eng’g Co. v. N. Am. Mfg. Co., 129 F.3d 1247, 1250 (Fed. Cir. 1997)].  There is no per se rule for determining whether a claim is not “substantially identical” [Laitram Corp. v. NEC Corp., 952 F.2d 1357, 1358 (Fed. Cir. 1991)]. The analysis includes examining “the claims of the original and the reexamined patents in light of the particular facts, including prior art, the prosecution history, other claims, and any other pertinent information” [Id. at 1362-63].  The determination is a legal one, and a claim is changed if its scope is changed [Tennant Co. v. Hako Minuteman, Inc., 878 F.2d 1413, 1417 (Fed. Cir. 1989)].

If a claim is not substantially identical, then a patentee may not seek damages for product sales prior to issuance of the reexamination certificate.  If damages have already been awarded, a defendant may seek to have damages vacated since the claims were void ab initio.  Because of the potential impact on damages, litigation counsel should consider filing reexamination requests on all patents-in-suit, if possible, and on all the asserted claims.

Accused infringers should consider the following CRU statistics as of June 30, 2010:

  • 75% of ex parte reexaminations initiated by a third party, reaching the issuance of reexamination certificate, resulted in some or all of the claims being canceled or amended.  Only 25% survived with all claims being confirmed. As of June 30, 2010, 7,586 ex parte reexamination certificates have been issued by the PTO.  This represents approximately 80% of all ex parte reexaminations granted.  Recall that ex parte reexaminations may also be initiated by request of the patent owner or the PTO Director.
  • 49% of inter partes reexaminations completed resulted in all claims being canceled. Combined with those amended, 92% resulted in some change to the claims.  Only 8% survived with all claims being confirmed. As of June 30, 2010, only 167 inter partes reexamination certificates have been issued.  This represents approximately 21% of all reexamination requests granted by the PTO.


  • Substantially Amended Claims
  • Doctrine of Intervening Rights
  • Vacating as Void Ab Initio