Aim: We present the case of a rare localization of the alveolar soft part of the sarcoma in the visceral organ. Introduction: Alveolar soft part sarcoma (ASPS) is a rare mesenchymal tumor typically occurring in young patients, more frequently in females. Common localization of ASPS is skeletal musculature of lower extremities. ASPS in visceral organs usually represents a metastasis from the more common primary location in skeletal muscles. ASPS is characterized by a tumor-specific translocation which causes the fusion of the TEF3 with a ASPL gene (also known as ASPSCR1). Case report: Female 47 years old was admitted to hospital due to abdominal pain. Urgent surgery was performed due to ileus. Ileal tumor was detected intraoperatively as a cause of ileus. Tumor was infiltrated whole intestinal circumference, with dimension 70mm x 47cm and evident perforation. Histology showed well-defined nests of pleomorphic cells separated by delicate fibrovascular septae. Within described nests there is a prominent lack of cellular cohesion, representing for the distinctive pseudoalveolar pattern. Immunohistochemical stadies were diffusely positive for TFE3 and focally positive for CD34 and alpha-SMA and negative for panCK, DOG-1, CD117, S-100, HMB45, Desmin. Immunopositivity for Ki67 was present in 20% of tumor cells. FISH analysis was done using locus specific dual color break-apart TFE3 (3 and 5 ) probe and rearrangement in the TFE3 gene was confirmed. Conclusion: Despite the fact that ASPS is rare mesenchymal tumor in visceral organs it have to be considered as possible diagnosis especially in cases with typical histological features and immunohistochemical profile. Definitive diagnosis of ASPS must be confirmed by FISH analysis.

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