Case of clear cell sarcoma in the left buttock in which serum neuron-specific enolase was a useful marker for monitoring disease progression.

We report a case of clear cell sarcoma (CCS) in the left buttock in which serum neuron-specific enolase (NSE) was useful as a biomarker of CCS progression. A 40-year-old man had a subcutaneous tumor, 1.7 cm in diameter, in the left buttock. Histopathology revealed that the tumor consisted of nests of polygonal or spindle-shaped cells with abundant clear cytoplasm delineated by fibrous septa in the subcutaneous tissue. There was cellular atypia but no melanin deposits. Immunohistochemically, the tumor cells were positive for HMB-45, Melan-A, S-100 protein and NSE. Reverse transcription polymerase chain reaction demonstrated Ewing's sarcoma oncogene-activating transcription factor 1 fusion transcripts in the tumor cells. CCS was diagnosed. There was no metastasis to the lymph nodes and viscera, and the patient was treated by surgical wide resection. The serum NSE levels increased before detection of distant metastasis and further increased in parallel with the expansion of metastasis. The present case suggests that serum NSE could be used as a biochemical marker in the clinical follow up of patients with CCS.