文摘
A 34-year-old man with intermittent chest pain had a 60-mm mass in the anterior mediastinum. A CT-guided needle biopsy revealed that the tumor was composed of atypical small cells and was positive for HMB-45 without cytoplasmic melanin pigmentation. These results suggested a diagnosis of malignant melanoma (MM) or clear cell sarcoma (CCS). EWS gene rearrangement was detected by fluorescence in situ hybridization, resulting in the definite diagnosis of CCS. Sarcomas originating in the mediastinum account for only 1?% of all sarcoma cases. CCS is a rare soft tissue sarcoma, which usually occurs in the tendons and aponeuroses and is often misdiagnosed as MM because of similar immunophenotypes. There is only one reported case of a primary CCS of the mediastinum. There is no standard treatment for CCS, but for metastatic MM, dacarbazine, ipilimumab, and BRAF-inhibitors can be treatments of choice. Thus, differential diagnoses are important to determine treatment strategies. Meticulous observation of skin lesions and pathological and molecular diagnoses, including EWS gene rearrangement, is recommended in cases with mediastinal tumors suspected of MM or CCS.