Teratoid Wilms' tumor: case report of a rare variant that can mimic aggressive biology during chemotherapy.

Teratoid Wilms' tumor is considered by some as a variant of Wilms' tumor containing at least 50% heterologous differentiated tissue. Fewer than 30 cases have been described. We report a 9-month-old boy with bilateral Wilms' tumors who did not respond to multiagent chemotherapy and underwent right nephrectomy that showed a teratoid Wilms' tumor.