Objective: Alveolar soft part sarcoma (ASPS) is characterized by distinctive histomorphology of variably discohesive epithelioid cells arranged in nests and translocation of t(x;17) (p11.2;q25) resulting in ASPSCR1-TFE3 fusion. The aim of the present study is to review the clinical, histopathological, and immunohistochemical profile of ASPS with a focus on unusual histological features.

Material and Method: The present study is retrospective and descriptive. All cases with a diagnosis of ASPS were retrieved with clinical and radiology details.

Results: 22 patients of ASPS were identified. The most common site was the lower extremity and the size range was 3-22 cm. 54.5% of the patients had metastasis, with the lung as the most common site. Metastasis preceded detection of primary tumour in two cases. All cases showed similar histopathology of monomorphic epithelioid cells arranged in nests encircled by sinusoidal vasculature. Architecturally, the organoid pattern (81.8%) was followed by the alveolar pattern. 68.2% of the cases showed apple bite nuclei as the predominant nuclear feature. Rare nuclear features included binucleation (n=13), multinucleation (n=8), pleomorphism (n=4), nuclear grooves in three cases and intranuclear inclusion in one case, mitosis (n=5), and focal necrosis (n=6). All cases were positive for TFE3 and negative for AE1/AE3, EMA, HMB45, PAX8, MyoD1, SMA, synaptophysin, and chromogranin. Only two cases showed focal S100 positivity while one showed focal desmin positivity.

Conclusion: Diffuse strong nuclear TFE3 positivity is sensitive for ASPS in an appropriate clinicoradiological context. Due to the high propensity for early metastasis, complete metastatic work-up and long term follow up is recommended.