A single lesion demonstrating features of eccrine poroma and poroid hidradenoma

A case of a single poroma lesion with the features of eccrine poroma and poroid hidradenoma is reported. The patient was a 61-year-old woman with a soft nodule, light brown in color, located on the posterior aspect of the right knee and containing a pigmented papular lesion in its center. The histological features of the papular lesion and the nodule were consistent with those of eccrine poroma and poroid hidradenoma, respectively. The eccrine poroma portion consisted mostly of poroid cells. The number of cuticular cells was slightly greater than that of poroid cells in the poroid hidradenoma portion. The cuticular cells in this portion as well as the poroid cells in both portions were immunohistochemically positive for epithelial membrane antigen. The findings in this case suggest that there is a close relationship between eccrine poroma and poroid hidradenoma and support the view that poroid hidradenoma is a type of poroma.