['Psoriasin (S100A7) has originally been described to be expressed by psoriatic keratinocytes possibly as a result of altered differentiation and inflammation. As psoriasin was found to be overexpressed in human breast and bladder cancer suggesting a role in tumour progression, we investigated the expression of psoriasin in human epithelial skin tumours.', 'Realtime reverse transcription-polymerase chain reaction experiments were performed to analyse the mRNA-expression levels of psoriasin together with involucrin as a marker for epithelial differentiation and interleukin-8 (IL-8) as a marker for inflammation in skin biopsy samples from patients with precancerous skin lesions (PSL, n = 6), squamous cell carcinoma (SCC, n = 11), basal cell carcinoma (BCC, n = 17), and healthy controls (n = 10).', 'Unexpectedly, mRNA expression levels for Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) revealed a variation of up to 600-fold in all cDNA-samples under investigation, indicating that GAPDH is not suitable as a housekeeping gene in human skin samples. Psoriasin mRNA expression was significantly up-regulated in samples of PSL, SCC and BCC. In situ hybridisation and immunohistochemical examinations identified psoriasin mRNA and protein expression in the differentiated layers of the epidermis. IL-8 mRNA expression was significantly up-regulated in SCC, however, there was no correlation between elevated levels of psoriasin and the expression of IL-8.'] Is psoriasin ( S100A7 ) significantly up-regulated in human epithelial skin tumours?