Metastasizing fibrous histiocytoma of the skin: a clinicopathologic and immunohistochemical analysis of three cases.

The clinicopathologic and immunohistochemical features of three metastasizing fibrous histiocytomas of the skin are presented. The first patient had a 1.3-cm nodule in the right thigh, with right inguinal lymph node metastases 19 years later. The second patient, who had a 3-cm nodule excised from his left thigh and inguinal lymph node metastasis after 4 months, had a favorable outcome 14 years after local radiotherapy and chemotherapy. The third had a 2-cm nodule in his neck, which recurred 16 months later. Four months later, cervical lymph node metastases were found. The patient was alive and well 26 months after initial surgery. All three primary skin tumors involved the dermis and subcutis, appeared well-delineated but nonencapsulated, were associated with some degree of epidermal hyperplasia, and showed features of aneurysmal/atypical or cellular fibrous histiocytoma. The number of mitoses ranged from 6 to 11 per 10 high-power fields. Recurrences and metastases showed morphologic features similar to primary lesions. Tumor cells were positive, at least focally, for CD 68, Ki-M1p, and Factor XIIIa, and occasionally for smooth muscle actin. Desmin, CD 34, S-100 protein, and cytokeratin stainings were negative. Primary neoplasms, recurrences, and metastases showed a Mib-1 labeling index of 10% or less. Cellular, aneurysmal, and atypical (pseudosarcomatous) fibrous histiocytomas of the skin can metastasize, yet they often show a protracted clinical course. Risk factors for metastatic dissemination include large size, high cellularity, aneurysmal changes, marked cellular pleomorphism, high mitotic activity, tumor necrosis, and repeated local recurrences.