OBJECTIVETo study the clinicopathologic features and differential diagnosis of alveolar soft part sarcoma (ASPS).

METHODSThe clinical data and pathologic features of 48 cases of ASPS were evaluated. Immunohistochemical study, PAS staining and fluorescence in-situ hybridization (FISH) were carried out in selected examples. Relevant literature was reviewed.

RESULTSAmongst the 48 cases studied, there were 17 males and 31 females, with male-to-female ratio of 1.0∶1.8. The age of patients ranged from 2 to 60 years (median=26 years). The tumor was most commonly located in deep soft tissue, especially that of lower extremities. Histologically, the tumor cells were arranged in alveolar or solid patterns and separated by sinusoidal vessels. They were large and contained abundant eosinophilic granules or crystals in cytoplasm. The nuclei were round to polygonal and vesicular, often with prominent nucleoli. Intravascular tumor extension was common. Some cases showed necrosis, hemorrhage and cystic changes. Immunohistochemical study showed that the tumor cells were positive for TFE3 (100%, 33/33). FISH assay was carried out in 4 cases and all of them had TFE3-ASPL gene fusion.

CONCLUSIONSASPS is a rare malignant neoplasm, often occurs in young patients. TFE3 is a useful immunohistochemical marker for diagnosis. The diagnosis is further confirmed by other markers.