BACKGROUND.
Eccrine porocarcinoma is an uncommon neoplasm of the intraepidermal sweat gland duct. METHODS. A case of porocarcinoma of the right heel in a male age 51 years is described with a review of pertinent literature. The surgically excised neoplasm was evaluated by routine histology and transmission electron microscopy. RESULTS. The porocarcinoma showed extensive nuclear pleomorphisms with frequent, multinucleated tumor giant cells, focal epidermotrophic spread within the epidermis, a peripheral, eccrine syringofibroadenoma-like growth pattern, and an origin in a contiguous eccrine poroma. Ultrastructurally, the squarnous tumor cells contained rare intracytoplasrnic lumens. CONCLUSIONS. The extensive nuclear pleomorphism with frequent tumor giant cells was an unusual feature of the porocarcinoma. Its epidermotrophic spread within the epidermis and its origin in a contiguous eccrine poronia supported the diagnosis of porocarcinoma. The eccrine syringofibroadenoma-like growth pattern in the periphery of the tumor was a unique and previously undescribed feature of the porocarcinoma. The presence of intracytoplasmic lumens in squamous tumor cells mimicked embryonic development of the intraepidermal sweat gland duct.