Malignant eccrine poroma. Case report and review of the literature.

A case of malignant eccrine poroma with lymph node metastases is described. The patient had a nodular growth of the right thigh 2 years before its first excision. Local recurrence in the scar occurred in 6 months, and by 8 months a right groin lymph node was involved. Subsequent skin nodules of the right thigh occurred over the next 12 months, associated with recurrent lymphedema of the leg. During several follow-up visits, associated malignancies were found including villous adenoma of the ascending colon and renal cell carcinoma of the right kidney, both typical histologically and unrelated to the cutaneous tumor. Subsequently, left inguinal lymph node disease histologically identical to the skin tumor was found. Clinical and histologic findings were similar to the 31 previous cases reviewed. Electron microscopic examination confirmed the presence of a ductal structure consistent with eccrine duct and a crystalline membrane-bound granule which may represent a specific marker for this rare tumor. The histologic features of this tumor are important to separate from other differential diagnostic possibilities which may have a quite different prognosis.