Dermatofibroma is a clonal proliferative disease

Benign fibrous histiocytoma of the skin or dermatofibroma (DF) has been reg arded as a fibrohistiocytic tumor. Whether DF is a neoplastic growth or a r eactive 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 dis ease. Fresh specimens of 13 DFs and 2 hypertrophic scars obtained from fema le patients were studied. The adjacent nonlesional skin tissues served as c ontrols. The clonal analysis was based on the methylation pattern of the po lymorphic X-chromosome linked androgen-receptor gene (HUMARA). Eight DFs an d 1 hypertrophic scar were heterozygous at the androgen receptor gene and c ould be analyzed. All 8 informative DFs showed a significant reduction in o ne of the allelic bands compared with the corresponding bands of the nonles ional 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.