HIDROACANTHOMA SIMPLEX.

Our purpose has been to draw attention to the existence of sudoriferous metaplasia in a number of superficial neoplasms of the skin. The neoplastic cells arise by an adnexal deviation of the rete cells ; the matrices which they form represent neoplastic primordia in which, under suitable conditions, differentiation into sweat glandular structures will occur. The structure of individual tumours is linked to the degree of adnexal deviation. Six structural variants can be recognized, two being benign and four malignant. In their histology many examples of benign hidroacanthoma simplex correspond with the intraepidermal basal cell epithelioma as classically described by Jadassohn, Among the tumours generally classed as seborrhoeic warts are a few which represent formes frustes of hidroacanthoma simplex. The cancers include examples of intraepidermal carcinoma and of Bowen's disease. Reasons are advanced for the prolonged in situ course of many of the latter. [ABSTRACT FROM AUTHOR]