Malignant hidroacanthoma simplex

A case of malignant hidroacanthoma simplex is described. Histological examination revealed that the malignant cells had arisen from a tumor cell nest of benign hidroacanthoma simplex and invaded the dermis. Two years and 7 months after the excision of the original thigh lesion, a groin lymph node metastasis was discovered. The metastatic tumor cells in the lymph node were histologically similar to the carcinoma cells in the original thigh lesion and had enzymatic and ultrastructural features resembling eccrine sweat duct.