Current topics of immunohistochemistry as applied to skin tumors.

Suppressor oncogene p53 is expressed more frequently in the nodular portion than the superficial spreading portion of the same melanoma. PCNA expression follows the same pattern but it is strongly expressed already in the superficial spreading portion. CD34 is found to label dermatofibrosarcoma protuberans. There is the mixture of negative strands but the immunostains are predominantly positive in the three cases studied. Neurogenic tumors are reactive but the intensity of staining is only moderate. Fibrous histiocytoma, dermatofibroma and other fibrohistiocytic tumors are non-reactive. CD34 is expressed in the outer root sheath of hair follicle below the sebaceous gland level. A case of piloepidermal cyst is CD34 positive. CD34 is expressed in vascular endothelial cells; not only hemangiomas but also lymphangiosarcoma is CD34 positive. A case of indeterminate cell histiocytosis following scabies and superficial variant of clear cell sarcoma are discussed as examples of new entities.