Rhabdomyosarcoma in patients older than 40 years of age.

The original diagnosis of rhabdomyosarcoma (RM) was critically evaluated by histology, immunohistochemistry, and electron microscopy in a retrospective series of 25 patients older than 40 years of age. Only two of the 25 patients (8%) were verified to have RM by strict criteria. By light microscopy, the true RM had a spindle or round cell appearance and were subtyped as embryonal RM, although some pleomorphism was present. Sarcomeric differentiation was revealed by electron microscopy, and desmin and muscle actin by immunohistochemistry. Both of these tumors arose in the urogenital organs, one in the urinary bladder and the other in the prostatic region. Both patients died within 3 months of the diagnosis. The other tumors not verified as RM were pleomorphic or spindle cell sarcomas (n = 17), ten of which were considered to represent malignant fibrous histiocytoma, or had desmin and/or muscle actin, and were verified as leiomyosarcomas by electron microscopy (n = 2). There were single cases of undifferentiated carcinoma, probable neuroendocrine carcinoma, extraskeletal osteosarcoma, and pleomorphic liposarcoma. The average survival for the non-RM tumor patients was 32 months. The results show that true RM do occur in the elderly, but they are very rare. Such tumors may have clinicopathologic properties similar to embryonal RM in children both in regard to the site of origin and to the histologic picture. True RM seems to carry a worse prognosis than other pleomorphic sarcomas, and this emphasizes the need for accurate diagnosis.