Immunohistochemical comparison of beta-catenin expression by human normal epidermis and epidermal tumors.

beta-Catenin, a cytoplasmic protein that binds directly to the intracellular domain of cadherin, controls various functions such as cell adhesion. In many human carcinomas, E-cadherin-mediated cell-cell adhesion is lost or disturbed and related to metastasis. The purpose of this study was to compare the expression of beta-catenin in the normal epidermal keratinocytes and samples from cutaneous benign and malignant epidermal tumors in 140 patients. Our study population consisted of 140 patients with benign or malignant epidermal tumors. Using immunohistochemical methods, we compared the expression of beta-catenin in their normal epidermal keratinocytes, and in samples from 61 benign (seborrheic keratosis, n = 33; verruca vulgaris, n = 14; keratoacanthoma, n = 14), and 79 malignant (Bowen's disease, n = 18; basal cell carcinoma, n = 33; squamous cell carcinoma, n = 28) epidermal tumors. beta-Catenin was found to be expressed in the cell membrane of normal keratinocytes. Compared to other cell components of the normal epidermis, basal cells showed the strongest beta-catenin expression in all 140 patients. While absent in three of 61 benign tumors, compared to normal basal cells, the expression of beta-catenin in the other 58 tumors was not significantly different; it was reduced in 71 of 79 malignant tumors (P < 0.0001). In Bowen's disease, the expression of beta-catenin on the tumor cell membrane was reduced, however, strong expression was seen in the nuclei and cytoplasm. Our results suggest that beta-catenin expression on the membrane of keratinocytes is associated with the differentiation of normal keratinocytes but not with their stage of differentiation, nor with the proliferation ability of epidermal tumor cells.