Malignant hidroacanthoma simplex. A light microscopic, ultrastructural, and immunohistochemical study of 2 cases

2 cases of malignant hidroacanthoma simplex are reported. Prominent ultrastructural findings were sparse tonofilaments and villous-like, interdigitating cytoplasmic processes connected by small desmosomes. Positive intracytoplasmic stain for carcinoembryonic antigen was found in 1 case. Benign and malignant eccrine poromas and hidroacanthoma simplex appear to be related neoplasms on the basis of ultrastructural and immunohistochemical findings.