MALIGNANT TRANSFORMATION OF BENIGN HIDROACANTHOMA SIMPLEX

A case of malignant hidroacanthoma simplex of the anterior aspect of t he right ankle in a 75-year-old man is reported. A specimen obtained i n 1987 showed the features of benign hidroacanthoma simplex, whereas t hat taken in 1991 revealed malignant transformation. We performed immu nohistochemical studies on these two specimens, and they suggest this tumor derives from the outer cells of intraepidermal ducts. The prolif erating cell nuclear antigen labelling index and argyrophil nucleolar organizer regions of these two specimens were also compared and correl ated with malignant transformation.