A rare soft tissue tumor characterized by a slow-growing, usually painless, subcutaneous nodule, predominantly located in the extremities, less frequently the trunk or head and neck region. Histopathologically, the lesion is well-circumscribed, lobulated, and composed of epitheloid, ovoid, or spindle cells arranged in a nodular and often syncytial pattern, with pseudoangiomatoid spaces and a peripheral fibrous pseudocapsule with a prominent lymphoplasmacytic cuff. The tumor is most common in the first two decades of life and usually follows an indolent course, although local recurrence may occur, while metastasis is rare.

Diaphyseal medullary stenosis with malignant fibrous histiocytoma is an autosomal dominant bone dysplasia characterized by pathologic fractures due to abnormal cortical growth and diaphyseal medullary stenosis. The fractures heal poorly, and there is progressive bowing of the lower extremities. In 2 families, affected individuals also showed a limb-girdle myopathy, with muscle weakness and atrophy. Approximately 35% of affected individuals develop an aggressive form of bone sarcoma consistent with malignant fibrous histiocytoma or osteosarcoma. Thus, the disorder may be considered a tumor predisposition syndrome (summary by Camacho-Vanegas et al., 2012).