Alveolar soft part sarcoma. A clinicopathologic and immunohistochemical study.

The histogenesis of alveolar soft part sarcoma (ASPS) has been investigated since its description. Twenty ASPS cases were analyzed for immunohistochemical content, with emphasis directed toward the paraganglial, Schwann cell, and muscle theories of histogenesis. In addition, the cases were examined for possible prognostic clinical features. The clinical characteristics of the patients were similar to those reported previously concerning average age (23 years); male:female ratio (1:1); and predominant primary site (lower extremity, nine cases). Despite a local recurrence rate of 20% and a metastatic rate of 68% (including four at presentation), the natural history was often indolent and relapse commonly occurred very late. The average follow-up period was 10.1 years. While the overall 5-year survival was 67%, only seven of 18 patients were alive without disease at last follow-up (1.7-32 years), and one patient died of tumor after a 28-year disease-free interval. Neither tumor size nor site appeared to affect prognosis. The tumors were analyzed immunohistochemically for neurofilament, S-100 protein, met-enkephalin, leu-enkephalin, acetylcholinesterase, alpha 1-antichymotrypsin, Factor VIII-related antigen, serotonin, lysozyme, neuron-specific enolase, myoglobin, cytokeratins, desmin, and vimentin. Except for weak vimentin immunoreactivity, no other antigenic expression was detected despite multiple repeated experiments with several antibodies. S-100 protein which is present in virtually all granular cell tumors was absent in the cases of ASPS. The lack of detectable expression of neurofilament, met-enkephalin and leu-enkephalin, and neuron-specific enolase is interpreted as evidence against the paraganglial theory of histogenesis. Similarly, the repeated absence of the muscle proteins, desmin and myoglobin, in contrast to a previous report, is interpreted as evidence against a myogenic origin.