The immunohistochemical expression of skin-derived anti-leukoproteinase (SKALP)/elafin in lung squamous cell carcinoma (SqCC) and in uninvolved bronchial epithelium was studied. The results were compared with the immunohistochemical staining of proliferating cell nuclear antigen (PCNA) and the TDT-mediated dUTP-digoxigenin nick end labeling (TUNEL) assay. SKALP/elafin was expressed in SqCC with high incidence (82.6%). By contrast, the expression was not observed in uninvolved bronchial epithelium. SKALP/elafin expression was located in the cell layers just underneath the cornified envelope of each cell nest, and DNA fragmentation was observed in the same cell layers. PCNA was expressed in the basal layer of each cornified envelope, and both expressions were clearly separated. Immunoreactive score of SKALP/elafin expression was significantly correlated with the differentiation and it tended to increase in accordance with the degree of differentiation. These results suggested that SKALP/elafin was possibly involved in the cell differentiation program, finally leading to keratinization in SqCC of human lung. SKALP/elafin may be a beneficial molecular target for detection or even the development of a new therapeutic method against cancer.

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