Malignant eccrine spiradenoma: a case report with pulmonary metastasis.

Malignant eccrine spiradenoma is an extremely rare sweat gland tumor. It may develop de novo or arise in pre-existing benign eccrine spiradenoma. However, most tumors are presented in the latter mode. The case of a 50-year-old man with malignant transformation from previously existing benign eccrine spiradenoma over his right lateral thigh is reported. Evidence for this diagnosis includes two distinct morphological components. One is the well demarcated, small round to oval benign eccrine spiradenoma and the other is the malignant element with sarcomatoid differentiation. Some foci of transition between the benign eccrine spiradenoma and the sarcomatoid part are evident and represents that the latter may arise from the former. Whether different morphological patterns influence the patients' outcome is still doubtful. However, the malignant eccrine spiradenoma is thought to have the capacity of metastasis and lethal potentiality.