Abstract
Alveolar soft part sarcoma (ASPS) is a very rare sarcoma, report <1% of all soft tissue tumor. Majority of cases were young adult and tumor occurred in lower extremities and trunk. Here, we present a case of 53-year-old Thai female with rapidly glowing mass over her right forearm. The magnetic resonance imaging scan demonstrated a hypervascular mass with multiple feeding vessels located in flexure tendon of right forearm. Ultrasound-guided biopsy revealed malignant poorly differentiated epithelioid neoplasm with clear cell feature and focal necrosis. Surgery may be considered the first-line treatment in localized ASPS and may potentially increase long-term survival. Complete surgical excision is the mainstay of treatment. TFE3 and Cathepsin K immunohistochemistry are useful in confirming a diagnosis of ASPS with a distinctive clinicopathologic features.