Differentiated rhabdomyomatous tumors after chemotherapy for metastatic testicular germ-cell tumors: a clinicopathological study of seven cases mandating separation from rhabdomyosarcoma.

To gain insight concerning prognosis, we investigated seven cases of post-chemotherapy retroperitoneal lymph-node dissections from patients with testicular germ-cell tumors that contained sizable nodules of differentiated skeletal muscle, but that lacked both a primitive cellular component and mitotic activity. The patients were 18-28 years old at the time of retroperitoneal lymph-node dissection. All had a previous non-seminomatous germ-cell tumor of the testis, five of which had a teratoma component. In one the testicular tumor had foci of embryonal rhabdomyosarcoma. The retroperitoneal lymph-node dissections were performed 0.2-4.7 years after orchiectomy, all following cisplatin-based chemotherapy, and contained rhabdomyomatous tumors that ranged from 0.8-5 cm. These consisted of nodular to diffuse aggregates of fetal-type rhabdomyocytes with central to peripheral nuclei and abundant, eosinophilic, fibrillary cytoplasm with occasional cross striations. Elongated myotubes with multiple nuclei in a common sarcoplasm occurred at least focally in all cases. Mild to moderate nuclear atypia, including nuclear enlargement and nucleolar prominence, was present, but mitotic activity, necrosis, and a primitive cellular component were absent. All but one retroperitoneal lymph-node dissection also contained other teratomatous elements. Follow-up in six patients showed three were disease free at 2.2-3.4 years; two developed recurrent teratoma at 1.3-3.7 years; and a sixth developed recurrent teratoma at 0.5 and 2 years, followed at 17 years by progressive tumor with elevated alpha-fetoprotein. No patient with available follow-up developed progressive sarcoma. We conclude that rhabdomyomatous tumors in retroperitoneal lymph-node dissection specimens after chemotherapy for metastatic testicular germ-cell tumors show clinical behavior similar to teratoma rather than rhabdomyosarcoma. We believe the most likely explanation for the finding of pure rhabdomyomatous tumors in this setting, a phenomenon sometimes termed 'cytodifferentiation,' is selective persistence of differentiated tumor cells because of chemotherapy.