CLDN4 and squamous cell carcinoma: There have been previous reports to indicate that claudin-4 is upregulated in primary breast (Kominsky et al, 2004; Tokes et al, 2005), ovarian (Rangel et al, 2003; Agarwal et al, 2005; Santin et al, 2005), prostate (Long et al, 2001; Sheehan et al, 2007) squamous cell carcinoma (Morita et al, 2004) and pancreatic cancers (Michl et al, 2001, 2003; Nichols et al, 2004; Sato et al, 2004) but is downregulated in gastric cancer (Lee et al, 2005).