Bilaterally multicentric synchronous Wilms' tumor: successful conservative treatment despite persistence of nephrogenic rests.

We report a case of synchronous bilateral Wilms' tumor in a girl with incomplete Beck-with-Wiedemann syndrome and hemihypertrophy. Multiple small tumors were present in both kidneys. The initial diagnostic biopsy showed stage I monophasic blastematous Wilms' tumor of favorable histology, with multiple perilobar nephrogenic rests (nephroblastomatosis). By flow cytometry, tumor was diploid, with an S-phase fraction of 13.9%. Dactinomycin and vincristine were begun as per the National Wilms' Tumor Study IV (18 week course). After 1 month, only a single small lesion was evident, which persisted unchanged. Excisional biopsy 5 months after beginning chemotherapy showed entirely necrotic tumor but apparently unaltered nephrogenic rests. After completing chemotherapy, the child has done well, with normal renal function and no evidence of disease 3 years after diagnosis. Management of stage V Wilms' tumor is tailored to the individual case, being as conservative as possible to spare renal parenchyma. Given the high incidence of coexisting nephrogenic rests in bilateral Wilms' tumor, careful follow-up is required, as these potentially premalignant rests may resist chemotherapy.