at any time during the enforceability of a patent any person may file a request for the USPTO to conduct a second examination of any claim of the patent on the basis of prior art patents or printed publications which that person states to be pertinent and applicable to the patent and believes to have a bearing on the patentability (see 37 CFR 1.501). In order for the request for reexamination to be granted, a substantial new question of patentability must be present with regard to at least one patent claim. The request must be in writing and must be accompanied by payment of a reexamination request filing fee as set forth in 37 CFR 1.20(c).