OBJECTIVETo study the clinical, pathological and immunohistochemical features of giant cell fibroblastoma (GCF), with emphasis on its differential diagnosis and histogenesis.

METHODSSeven cases of GCF were investigated by light microscopy and immunohistochemistry.

RESULTSSix cases occurred in children, and one occurred in a 35 year-old adult (mean 9.4 years). Five were male and two were female. Clinically, all cases appeared as slowly growing painless nodules located in the dermis or subcutis of the trunk and extremities. Microscopically, the poorly circumscribed tumor was composed of a proliferation of slightly to moderately atypical spindle cells which were arranged in parallel or wavy fascicles, and embedded in a fibromyxoid to collagenous background. The pathognomonic feature consisted of irregular distributed cleft-like or sinusoid-like pseudovascular spaces lined with a discontinuous layer of pleomorphic spindle cells and multinucleate giant cells. There was transition in shape between these two cells. Immunohistochemially, both cells expressed vimentin and CD34. Follow-up information in five cases showed local recurrences in two cases.

CONCLUSIONS(1) GCF is a distinctive fibroblastic tumor of intermediate malignancy that occurs predominantly in children. Recognizing its clinical and pathological characteristics is important to avoid misdiagnosis with other lesions with similar features. (2) GCF shared clinical, immunohistochemical and cytogenetic features with its adult counterpart-dermatofibrosarcoma protuberans (DFSP). The additional coexistence of GCF and DFSP areas in some primary cases and the reciprocal transformation in recurrent tumors all suggest that they are two closely related entities, possibly representing two members of the CD34 positive dendritic neoplasms.