Alveolar soft part sarcoma (ASPS) is a rare, slow-growing soft tissue sarcoma. Although it has been described in a variety of locations, it most commonly develops on the lower extremities in adults and in the head and neck region of children. ASPS generally presents as a soft, pain-less lump that is often not associated with any additional signs and symptoms. In many cases, the condition is not diagnosed until the affected person develops symptoms of metastasis to other sites such as the lungs, bones, central nervous system and/or liver. The underlying cause of ASPS is poorly understood. Most cases occur sporadically in people with no family history of the condition. ASPS is generally treated with surgery; radiation therapy and/or chemotherapy may be considered if the tumor returns.