Disseminated porokeratosis accompanying multicentric Bowen's disease. Characterization of porokeratotic lesions progressing to Bowen's disease.

Multicentric Bowen's disease developed in a 73-year-old man in areas involved with disseminated porokeratosis. The porokeratotic lesions were brownish; some were small and solitary, and others were coalesced and of variable size. Some lesions were erythematous. The histologic findings of the small, solitary or brownish, coalesced lesions were those of porokeratosis without apparent dysplasia; however, the erythematous coalesced lesions revealed epidermal dysplasia. Study revealed DNA ploidy abnormalities in the epidermal cells of these porokeratotic skin lesions. The skin lesions progressed in their degree of DNA ploidy abnormality from small solitary lesions to brownish coalesced ones and further to erythematous, coalesced ones. These observations suggest the direct and sequential growth of potentially malignant neoplastic clones in the patient's porokeratotic skin lesions and explain the multicentric development of Bowen's disease.