Four studies involving a total of 30, 48, 101, and 141 specimens have reported that the downregulation of claudin-1 is linked to unfavorable tumor characteristics, a poor prognosis, and/or biochemical recurrence (Sheehan et al., 2007; Väre et al., 2008; Seo et al., 2010; Szász et al., 2010). This evidence concerns the gene CLDN1 and neoplasm.