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Benign fibrous histiocytoma of the skin or dermatofibroma (DF) has been regarded as a fibrohistiocytic tumor. Whether DF is a neoplastic growth or a reactive process has not been settled. Since a neoplastic process is clonal in nature, clonal analysis of DF was conducted to see if DF is a clonal disease. Fresh specimens of 13 DFs and 2 hypertrophic scars obtained from female patients were studied. The adjacent nonlesional skin tissues served as controls. The clonal analysis was based on the methylation pattern of the polymorphic X-chromosome linked androgen-receptor gene (HUMARA). Eight DFs and 1 hypertrophic scar were heterozygous at the androgen receptor gene and could be analyzed. All 8 informative DFs showed a significant reduction in one of the allelic bands compared with the corresponding bands of the nonlesional tissue after Hha I digestion. Therefore, DF is a clonal proliferative disease. In contrast, 1 hypertrophic scar showed a polyclonal pattern of X-chromosome inactivation. We conclude that DF is a clonal disease favoring a neoplastic process.

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