Primary alveolar soft‐part sarcoma of the mediastinum: a clinicopathological and immunohistochemical study of two cases

AIMS: Primary alveolar soft part sarcomas originating within the thoracic cavity are rare. The cases herein described highlight the ubiquitous distribution of this neoplasm and the importance of considering this tumour in the differential diagnosis of mediastinal tumours. METHODS AND RESULTS: Two cases of alveolar soft-part sarcoma of the mediastinum are presented. The patients are two men of 22 and 23 years of age. Clinically, the patients presented with symptoms of chest pain. One tumour was in the anterior mediastinum while the second tumour was in the posterior mediastinum. Even though the bulk of the tumours were in mediastinal locations, both patients had pulmonary metastases at the time of diagnosis. Histologically, both tumours showed the classic morphology of alveolar soft part sarcoma, i.e. a proliferation of large polygonal cells with round to oval nuclei, prominent nucleoli and moderate amounts of eosinophilic cytoplasm arranged in a prominent alveolar pattern. Periodic acid-Schiff stains showed the characteristic diastase-resistant intracytoplasmic crystals. Immunohistochemical studies showed focal myoglobin reactivity in one case, while cytokeratin, vimentin, S100 protein, chromogranin, synaptophysin, neurofilaments, leu-enkephalin, desmin, smooth muscle actin and muscle-specific actin were negative in both cases. The patient with the anterior mediastinal tumour died of disease 14 months after diagnosis, and the patient with the posterior mediastinal mass remained well for at least 15 years and was later lost to follow-up. CONCLUSIONS: As has been observed in other anatomic areas, namely soft tissues, alveolar soft part sarcomas may follow an uncertain natural history. Interestingly, in our cases, the tumour in the anterior mediastinum followed a fatal course raising the possibility that the anatomic location of the tumour may have play a role in the behaviour of the tumour.