Immunohistochemical analysis of keratin distribution in eccrine poroma.

Although eccrine poroma has been thought of as a neoplasm of the intradermal eccrine duct, this interpretation has not been entirely confirmed. In this study, twenty-five cases of eccrine poroma were retrieved and analyzed by immunohistochemical techniques, using various kinds of monoclonal antikeratin antibodies. Comparative immunohistochemical observations of eccrine poroma and normal eccrine glands revealed that the poroma cells expressed immunophenotypes similar to those of the basal cells of dermal eccrine ducts. Sweat-ductlike structures showed similar staining patterns to those observed in the inner cells of dermal eccrine ducts. Some cystic spaces were similar to those observed in the secretory cells of eccrine glands. Eccrine poroma is, therefore, speculated to originate via the proliferation and expansion of the basal cells of eccrine ducts, although it is very difficult to prove the histogenesis. Some tumor cells may differentiate toward inner cells of the eccrine ducts, forming ductal lumina, whereas other tumor cells differentiate toward eccrine secretory regions, forming some cystic spaces.