Immunohistochemical examination of an orbital alveolar soft part sarcoma

· Background: A 32 year-old male patient had a 6-week history of left-sided proptosis. Computer tomography revealed a 16×15×15 mm smooth and well-defined mass between the optic nerve and the medial and superior rectus muscles in the left orbit. · Methods: The tumour was excised via a cranio-medial orbitotomy approach. · Results: Histopathological examination, immunohistochemistry and electron microscopy findings were consistent with an alveolar soft part sarcoma. Immunohistochemical staining showed positive immunoreactivity for neurone-specific enolase, vimentin, p53 (30%), p21 (10%) and cyclin D1 (20%), and negative immunoreactivity for CD45, cytokeratins, S-100 protein, glial fibrillary acidic protein, synaptophysin, chromogranin, calcitonin, serotonin, thyreoglobulin, desmin, myosin, actin, HMB-45, pRB, p16 and BCL-2. The growth fraction of the tumour cells was 3%. At examination 4 years after surgical excision, there was no evidence of local recurrence or for metastases. · Conclusion: Alveolar soft part sarcoma of the orbit is a rare malignant tumour best controlled by surgery. The unpredictable behaviour of these neoplasms, however, indicates the need for long-term follow-up. Received: 2 July 1998 Revised version received: 31 August 1998 Accepted 3 September 1998