A 40-year-old man with high fever, hemoptysis, and fatigue showed a 10-cm mass in the middle and lower lobes of the right lung on computed tomography. Histological examination of transbronchial biopsy specimens showed sheets of small round tumor cells and mild staining for CD99. Primary Ewing sarcoma was suspected, and a trimodality therapy consisting of chemotherapy, intensity-modulated radiation therapy, and right pneumonectomy with surrounding tissue resection was performed. In surgical specimens, negative outcome of NKX2.2 in immunostaining and EWSR1 rearrangement in fluorescence in situ hybridization did not support the diagnosis of Ewing sarcoma. Positive immunostaining for MDM2 and CDK4 led to a diagnosis of dedifferentiated liposarcoma, which probably originated from an adipose tissue of the right perihilar mediastinum, and then invaded the lungs. The postoperative course was uneventful, without recurrence for more than 16 months.

一名 40 岁男性，高烧、咯血和乏力，计算机断层扫描显示右肺中叶和下叶有 10 厘米的肿块。经支气管活检标本的组织学检查显示小圆形肿瘤细胞片和 CD99 轻度染色。怀疑原发性尤文肉瘤，并进行了由化学疗法、调强放射疗法和右肺切除术和周围组织切除组成的三联疗法。在手术标本中，NKX2.2 在免疫染色和EWSR1中的阴性结果荧光原位杂交的重排不支持尤文肉瘤的诊断。MDM2 和 CDK4 免疫染色阳性导致去分化脂肪肉瘤的诊断，该脂肪肉瘤可能起源于右肺门周围纵隔的脂肪组织，然后侵入肺部。术后病程平稳，16个月以上无复发。