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.