Porokeratosis as a premalignant condition of the skin. Cytologic demonstration of abnormal DNA ploidy in cells of the epidermis.

Clinical evidence has accumulated of malignant epithelial tumors developing on the lesions of porokeratosis. To determine the cytologic basis for the malignant change of porokeratosis, the nuclear DNA content of epidermal cells from porokeratotic lesions was measured using microfluorometry. A total of 42% of 33 porokeratotic skin lesions in eight of the 16 patients showed DNA polyploidization in the epidermis. Most of the porokeratotic skin lesions, with or without DNA polyploidization, increase cell proportions in the S and G2/M phase range. DNA indices of cells from these porokeratotic lesions distributed widely from the level of normal control epidermis to that of malignant epidermal conditions. These findings suggest that porokeratosis is undergoing the neoplastic process, and is a precursor of malignant tumors.