Epidemiology
A rare sarcoma of adolescents and young adults, with a typical musculoskeletal presentation as a deep mass in a limb or the pelvis. It can grow slowly and still metastasize, so systemic surveillance must not depend only on the size of the primary tumor.
Basic features
It is usually highly vascular and slow-growing, but it can metastasize even when the primary tumor is relatively indolent. The diagnosis is confirmed by the characteristic ASPSCR1::TFE3 fusion (nuclear TFE3 expression), which is needed both to tell it apart from other tumors that look similar and to access the therapies specific to this sarcoma.
Usual treatment
Local removal is combined with systemic surveillance; in advanced disease, VEGFR inhibitors (for example, pazopanib) and immunotherapy with checkpoint inhibitors are used (atezolizumab is approved specifically for advanced alveolar soft part sarcoma).
Outcomes and prognosis
Short-term survival is relatively good in localized disease, but it declines over the long term because the tumor often metastasizes; the risk of lung or brain metastasis calls for prolonged follow-up and appropriate imaging.