Anaplastic sarcoma arising in a mature metachronous bilateral Wilms' tumor after irradiation and chemotherapy. Spontaneous versus induced malignant change.

A 1-year-old male infant developed a classic Wilms' tumor of the left kidney. Treatment consisted of a left nephrectomy, chemotherapy, and irradiation to the left flank and associated abdomen. Two years later, a mass in the right kidney was discovered; open renal biopsy demonstrated a mature Wilms' tumor consisting entirely of rhabdomyomatous elements in the biopsy specimen. The patient was given a second course of chemotherapy and 2000 rad to the right flank. Over the next 8 years, the mass continued to grow without evidence of metastatic spread. Renal function deteriorated secondary to compression of the surrounding normal renal parenchyma by the enlarging tumor; creatinine clearance from the solitary kidney decreased from 120 ml/min to 40 ml/min during the 12 months prior to removal of the lesion. Via a nephron-sparing procedure, the 3400 g tumor measuring 19 cm X 16 cm X 9 cm was enucleated from the right kidney without compromise to the remaining normal tissue. Pathologic examination of the surgical specimen revealed a mature Wilms' tumor with a malignant anaplastic sarcoma arising in the central portion. Postoperatively, the patient received a third course of chemotherapy with no irradiation to the tumor bed. Currently, he is disease-free with normal renal function more than 20 years after diagnosis of the metachronous bilateral Wilms' tumor. This is the first reported case of an anaplastic sarcoma arising within a Wilms' tumor; this individual also is the longest surviving patient with metachronous Wilms' tumor. The various possibilities regarding the development of the anaplastic sarcoma within the Wilms' tumor of the right kidney are discussed, including the possible role of chemotherapy and irradiation in the development of a second malignancy.