Immunohistochemical analysis of cytokeratin expression in apocrine cystadenoma or hidrocystoma

Apocrine cystadenoma is a benign sweat gland tumor which consists of various histologic types of epithelium: epithelium with decapitation secretion, pseudostratified epithelium, and flattened epithelium. Immunophenotypes, especially the expression of cytokeratins, in 8 cases of this tumor were examined immunohistochemically, because the nature or differentiation of each epithelium is not well known. The following antibodies were used as primary antibodies: those against involucrin, smooth muscle actin, and human milk fat globulin respectively, and 15 kinds of monoclonal anti-cytokeratin antibodies. Although the staining pattern varied from case to case according to the proportion of each epithelium, these epithelia, except for the flattened epithelium, revealed invariable staining patterns. The staining pattern in the epithelium with decapitation secretion and the pseudostratified epithelium was similar to that in the secretory portion including myoepithelial cells and the junction of the excretory ductal portion with the secretory portion, respectively. However, the flattened epithelium, probably due to intraluminal pressure, showed various staining patterns similar to that in each portion of the apocrine gland. Based on the above observations, we confirmed that apocrine cystadenoma was a complex tumor differentiating into each portion of the apocrine gland, i.e. the dermal duct, the junction of the excretory ductal portion with the secretory portion, and the secretory portion.