<![CDATA[Introduction: Rhabdomyosarcoma (RMS) is a malignant tumor that develops from mesenchymal cells, very rare in adults, approximately only 1-2%. Sclerosing Rhabdomyosarcoma (ScRMS) includes as newer subtypes of RMS, forming 5-10% of all RMS cases. RMS very rare occurs in the mediastinal, the predilection generally in extremity, genitourinary, head and neck region. RMS in adults has a poorer prognosis than paediatric and other high-grade sarcomas in adults. Case Presentation: A 47 years-old man with complaints of shortness of breath and left chest pain 4 months before admitted to the hospital. Thorax-CT suggests anterior mediastinal tumor with pericardial effusion, bilateral pleural effusion and venous cava superior syndrome (VCSS). The patient underwent open biopsy, radiotherapy, thoracocentesis and pericardiocentesis. Immunohistochemistry Desmin(+), CD45(-), CK(-), Myogenin(+), suggest a ScRMS dd Malignant Tryton Tumor, then H3K27Me3(+), SOX-10(-) established ScRMS. He started chemotherapy with Carboplatin-Etoposide regimen. After third series chemotherapy, RECIST CT examination showed progressive disease, patient then continued second line chemotherapy with Paclitaxel but also results to progressive disease. Conclusions: Pure mediastinal ScRMS in adults is extremely rare, with aggresive behaviour. Awareness of adults RMS is important due to its prognosis that rapidly progressive cause death and there is no standart regimen for adults RMS. Keywords: Sclerosing Rhabdomyosarcoma, Mediastinal Rhabdomyosarcoma]]>
