Giant cell tumor of the skin: a morphologic and immunohistochemical study of five cases.

Giant cell tumor (GCT) of the skin is a rare entity that possesses similar gross and histologic features to GCT of bone. When located predominantly in the dermis GCT has been mistaken for benign fibrous histiocytoma and atypical fibroxanthoma. We report the clinical, morphologic, and immunohistochemical features of five cases of GCT of the skin. With one exception, all tumors are confined to the dermis. Patients' ages range from 6 to 78 years (median, 73 years) with a male to female ratio of 3:2. Gross and histologic features of the lesions are similar to those of GCT of bone (eg, brown fleshy tumor and a biphasic population of mononuclear cells admixed with osteoclast-like giant cells, respectively). The nuclei of the giant cells are similar to those of the mononuclear cells. A fascicular pattern with focal storiform arrangement of spindle neoplastic cells is noted in two cases. The osteoclast-like giant cells and some of the mononuclear cells are strongly positive for CD68, alpha-1-antitrypsin, and alpha-1-antichymotrypsin. Only the mononuclear cells express smooth muscle actin focally in one case. Both the osteoclast-like giant cells and the mononuclear cells are negative for cytokeratins (AE1/AE3 and CAM5.2) and S-100 protein in all cases. One patient developed lung metastases at presentation and local recurrence 4 months status post surgery. All patients are without evidence of disease 1 month to 12 years status post surgery. Cutaneous GCTs are low-grade sarcomas that can recur locally and infrequently metastasize. These tumors should be distinguished from a variety of cutaneous neoplasms that contain multinucleated giant cells.