Benign fibrous histiocytoma of subcutaneous and deep soft tissue: a clinicopathologic analysis of 21 cases.

Twenty-one cases of benign fibrous histiocytoma arising in noncutaneous soft tissue are reported. These tumors presented most often in young to middle-aged adults with a predominance in males. They originated in deep subcutis (16 cases), skeletal muscle (three cases), and mesentery (two cases). The most common sites of incidence were the lower limb (eight cases) and head and neck region (six cases). Four of 12 cases with follow-up (median 3.0 years) recurred locally; all had originated in the subcutis. None metastasized. These lesions are generally larger and better circumscribed than their cutaneous counterparts. They are also usually more monomorphic and have a more consistent storiform pattern than the latter. A pericytomalike vascular pattern (six cases), xanthoma cells (six cases), and multinucleate giant cells (six cases) may be prominent. Hyaline or myxoid degeneration of the stroma is common. Rare features include small foci of necrosis and intravascular growth. Immunohistochemically, deep benign fibrous histiocytoma shows no evidence of true monocyte/macrophage differentiation and its histogenesis remains uncertain. The differential diagnosis includes malignant fibrous histiocytoma, dermatofibrosarcoma and hemangiopericytoma.