Histogenesis of clear cell hidradenoma: immunohistochemical study of keratin expression.

The expression of cytokeratins in 10 cases of clear cell hidradenoma, including 3 cases of solid cystic hidradenoma, were examined using 21 kinds of monoclonal antibodies. We divided them into three histologic patterns: massive nests with a few lumina (M nests), nests with some tubular lumina (L nests), and nests in solid cystic hidradenomas (S nests). All hidradenomas showed similar immunoreactivities to those in the lower dermal ducts or secretory cells of normal eccrine glands. With antibodies against simple epithelial cytokeratins (CKs 7, 8, 18, and 19), however, different immunostaining was noted among the three histologic patterns. Namely, the M nests failed to react to them, although some luminal cells in the L nests revealed a positive staining. Furthermore, a majority of luminal cells in the S nests revealed a positive staining with them. Therefore, we think that the luminal cells in solid cystic hidradenoma mainly differentiate toward the secretory cells, and that the M nests mainly differentiate toward the dermal duct. Those in the L nests are thought to differentiate toward the dermal duct and the secretory cells. The proportion of the differentiation toward luminal cells of dermal ducts to the differentiation toward secretory cells was the main difference among the three nests. In addition, there was no difference in immunophenotypes between clear cells and epidermoid cells in the two kinds of hidradenomas.