Medallion-like dermal dendrocyte hamartoma is a newly described and rare clinical and pathological entity. This congenital, round, erythematous and atrophic lesion in the thoracic area is histologically characterized by a CD34+ dermal and hypodermal spindle-cell infiltration. We describe the clinical, histopathological, cytological and molecular features of three cases of dermal dendrocyte hamartoma. In all the cases, atrophic congenital dermatofibrosarcoma protuberans (DFSP) was the first histological diagnosis. In one case, wide surgery had been performed on the basis of the clinical and histological presentation. The histological pattern was similar in all the cases: epidermal atrophy and a spindle to ovoid cell proliferation in the dermis and in the subcutaneous fat. Immunochemical staining for CD34 and factor XIIIa was positive. Cytogenetic and molecular studies were performed; no chromosomal abnormality nor translocation t(17;22)(q22;q13) was observed. Fluorescence in situ hybridization analysis did not reveal the DFSP fusion gene COL1A1-PDGFB. We observed that the main diagnostic pitfall of medallion-like dermal dendrocyte hamartoma is atrophic congenital DFSP due to clinical and histological similarities. We emphasize that molecular studies to eliminate the t(17;22)(q22;q13) translocation of DFSP may provide determinant elements for diagnosis in order to avoid unnecessary mutilating surgery.

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