The growing teratoma syndrome: an unusual manifestation of treated, nonseminomatous germ cell tumors of the testis.

Residual masses are a common finding after chemotherapy for retroperitoneal and other metastases from nonseminomatous germ cell tumors of the testis. These may contain mature teratoma, fibrotic tissue, or tumor. Mature teratoma, which is unresponsive to chemotherapy, may result from evolution of a malignant lesion during treatment, or it may represent a metastasis from a focus of mature teratoma in the primary testicular tumor. An enlarging retroperitoneal mass during the course of chemotherapy is usually due to treatment failure but rarely may be due to an enlarging mature teratoma, the so-called growing teratoma syndrome. This report concerns five patients with nonseminomatous germ cell tumors metastatic to the retroperitoneum in whom mature teratomas were found at surgery. These tumors had grown despite the administration of combination systemic chemotherapy, and the cystic component had increased in size. Three patients had evidence of urinary tract compression, three had vascular compression or displacement, and one had gastrointestinal compression. The retroperitoneal mass was excised in each patient, and all are alive 4-27 months after surgery without evidence of recurrence. Growing mature teratoma is unresponsive to chemotherapy but is cured by surgical excision. The possibility of the growing teratoma syndrome should be considered so that these lesions can be treated appropriately.