Diagnostic results at 27 years of age. (a) Chest computed tomography findings at the time of recurrence. A well-defined round mass is seen on the right upper lobe. (b) Resected specimen at the time of recurrence. The surgical specimen is a 55 × 40 × 40-mm soft tumor. The surface is smooth. The cut surface demonstrates a yellow-white, solid component with hemorrhage and focal necrosis. (c) Histopathological findings (hematoxylin-eosin, ×200). The tumor was composed of small round tumor cells that showed a rosette-like arrangement around the vessels. (d) Immunohistochemical staining for CD99 (×200). The tumor cell membrane stained positively for CD99.