Alveolar soft part sarcoma. A clinicopathologic and immunohistochemical study of 12 cases.

Twelve cases of alveolar soft part sarcoma (ASPS) were reviewed. Seven of them arose primarily in the lower extremities, three in the head and neck region, and two in other parts. ASPSs in the head and neck region occurred in children before 10 years of age, whereas ASPSs in the other regions occurred in rather older patients. Moreover, ASPSs of the head and neck were relatively small in size, and were diagnosed earlier than those in other regions. Histologically, six cases (including all the head and neck cases) contained considerable area of small and indistinct alveolar structures. Four cases showed remarkable cellular pleomorphism. Immunohistochemical demonstration of vimentin, desmin, the beta-subunit of enolase and the MM isozyme of creatine kinase, together with the absence of immunoreactive cytokeratin, supported the myogenic nature of this rare tumor. A small number of S-100 protein-positive tumor cells were also observed. Follow-up data for these cases disclosed that the tumors containing considerable area of small alveoli and uniform small tumor cells formed distant metastases at an early stage.