Primary alveolar soft part sarcoma of bone

Aims: Alveolar soft part sarcoma is a distinct, rare soft tissue tumour occ urring primarily within the skeletal muscles or musculofascial planes in yo ung adults. Primary involvement of bone is extremely rare. We report on six patients with alveolar soft part sarcoma occurring primarily in bone. Methods and results: Thorough clinical and radiographic examinations were d one to rule out any other primary site. The patients were four women and tw o men aged 17-35 years (mean, 24.5 years). The primary site of the tumour w as the femur in three patients, the ilium in one and the fibula in two. In one of the patients with fibular involvement, the tibia was also involved b y direct extension. Of the long bone lesions, three were centred in the met aphysis and one in the diaphysis. Radiographically, all of the lesions demo nstrated an osteolytic pattern of bone destruction with ill-defined margins and a wide zone of transition between the lesion and adjacent normal bone. Microscopically, all tumours showed the typical histological pattern of al veolar soft part sarcoma. Diastase-resistant, periodic acid-Schiff-positive crystalline structures were identified within the cytoplasm and confirmed ultrastructurally. Immunohistochemically, a keratin stain was negative in a ll cases; there was positive staining for MyoD1 in the cytoplasm but not; t he nuclei. Distant metastasis developed in four patients; one died. Conclusion: Alveolar soft part sarcoma arising in bone is extraordinarily r are but should be considered in the differential diagnosis of metastatic hy pernephroma in a young patient.