Mixed carcinoma in situ: an immunohistochemical study.

A case of mixed carcinoma in situ, of the skin, is presented. The lesion, located on the right temple of a 71-year-old man, showed histologic features of Bowen's disease and extramammary Paget's disease. This case suggests that Bowen's disease and extramammary Paget's disease may arise from pluripotential adnexal epithelium capable of keratinocytic and glandular differentiation. Utilization of the peroxidase-antiperoxidase technique for demonstrating carcino-embryonic antigen was performed in order to identify the component interpreted as extramammary Paget's disease. This procedure is apparently more sensitive than the commonly employed histochemical stains for demonstrating glandular differentiation.