Clear cell sarcoma arising in the transverse colon.

A case of clear cell sarcoma (CCS) arising in the transverse colon is presented. The tumor consisted of sheets or small nests of epithelioid malignant cells possessing pleomorphic nuclei with one or more prominent nucleoli and ample clear or slightly eosinophilic cytoplasm. Some of the tumor cells contained various amounts of melanin pigments that were confirmed by histochemical and ultrastructural examinations. Immunohistochemical examination showed a positive immunoreactivity for HMB45 and S-100 protein. A metastatic nodule, which was found 9 months after surgery, showed similar histological findings to those of the primary one but lacked melanin pigments. Reverse transcriptase- polymerase chain reaction using total ribonucleic acid obtained from metastatic nodule demonstrated the presence of EWS-ATF-1 fusion gene. Based on these findings, the present case tumor is a CCS of the colon.