Cytokeratin expression in malignant Triton tumor.

A malignant Triton tumor in a 9-year-old boy is described. The first biopsy which was taken from the thenar prominence was diagnosed as a monophasic fibrous synovial sarcoma based on the finding of a spindle cell neoplasm with plump nuclei and cytokeratin expression. The true nature of the tumor became apparent when a second biopsy was investigated. In this specimen a rhabdomyosarcomatous component was found in association with a spindle cell sarcoma fulfilling the criteria of a malignant schwannoma. Immunohistochemical staining using antibodies against vimentin, desmin, muscle-specific actin, cytokeratin, glial fibrillary acidic protein, protein S-100, Leu 7 and myoglobin served to distinguish the two tumor components and documented the possible reactivity of malignant Triton tumor for cytokeratins.