S–100 protein‐positive cells in hidrocystomas

The histogenesis of hidrocystomas was examined by the use of immunostaining for S-100 protein. In normal sweat glands, S-100 protein was found exclusively in the secretory cells of eccrine glands, whereas this protein was not present in the other parts of eccrine glands or at any levels of the structure of apocrine glands. On the bases of this immunostaining pattern in normal sweat glands, we attempted to correlate the origin of 8 cases of hidrocystoma to the presence of S-100 protein-positive cells. S-100 protein was detected in the cells of one solitary eccrine hidrocystoma, but not in those of 2 cases of "classic", multiple-lesion type of eccrine hidrocystoma. This indicated that the former arose from the secretory portion of the eccrine gland and the latter from the eccrine ductal cells. Two of the 5 cases of apocrine hidrocystoma showed positive staining in a part of the lining cells of the cyst wall, while the other 3 cases were negative to this protein. This finding suggests that some of the tumors diagnosed morphologically as apocrine hidrocystoma differentiate in the direction of eccrine secretory cells. In addition to S-100 protein, we also surveyed for the presence of carcinoembryonic antigen (CEA), and all cases examined were consistently positive to this substance. The detection of S-100 protein was considered to be more helpful in classifying hidrocystomas than that of CEA.