Peripheral nerve tumors with rhabdomyosarcomatous differentiation (malignant “triton” tumors)

Three peripheral nerve sheath tumors are reported which showed an intermingling of schwannian elements and rhabdomyosarcoma, a type of compound tumor first described by Masson in 1932. One of the patients had von Recklinghausen's disease. The tumor in two patients showed pleomorphic rhabdomyosarcoma, while in a third patient it grew partially as an embryonal rhabdomyosarcoma. All three tumors contained areas of malignant schwannoma, but, in this latter case, the rhabdomyosarcoma appeared to arise from an area of benign Schwann cell growth. Two of the patients died following spread of the malignant muscle component. All previously reported examples of this tumor developed in individuals showing stigmata of von Recklinghausen's disease. Data from our three cases and from seven cases from the literature indicates the tumor to be highly malignant. Of the nine patients with follow-up, seven were dead within 3 to 20 months of their diagnosis. Those recurrent tumors or metastases that were examined histologically (four cases) showed rhabdomyosarcoma.