Abstract 844 Hematology-Oncology II Poster Symposium, Sunday, 5/2

INTRODUCTION Approximately 1% of children with unilateral Wilms tumor develop contralateral disease. We assessed the demographic and histologic features associated with metachronous bilateral Wilms tumor (BWT) of children registered on the first four National Wilms Tumor Studies (NWTS).

METHODS The primary endpoint for evaluation was the first appearance of Wilms tumor in the remaining kidney. The cumulative risk of contralateral disease as a function of time since initial presentation was calculated as 1 minus the Kaplan Meier estimate of remaining free of contralateral disease. A matched case-control study was performed to evaluate whether the presence and type of nephrogenic rests (NRs) were associated with metachronous BWT.

RESULTS Fifty-eight of 4,669 registered children, all of whom had received post-operative chemotherapy, developed metachronous BWT; 38 of 2,445 females (expected 30.2) versus 20 of 2,224 males (expected 27.8) (p= 0.04). There was a pronounced decline in the risk of contralateral Wilms tumor development with increasing age at diagnosis. At 6 years from initial diagnosis, the cumulative incidence of contralateral tumor development for those aged 0-11 months at diagnosis was 4%; 12-23 months 1.4%; 24-47 months 1.2%; and >48 months <1% (p<0.0001). Patients with NRs had also an increased risk of developing metachronous BWT. The combination of young age at diagnosis and NRs carried the highest risk: 20 of 206 children <12 months of age with NRs, as compared to 0 of 304 >12 months of age with NRs (p<0.0001). Data from the matched case-control study confirmed the increased relative risk associated with young age and the presence of NRs.

RECOMMENDATIONS Abdominal ultrasonography should be performed at least every 3 months for 6 years in those <48 months of age at initial diagnosis. For children >48 months of age at initial diagnosis abdominal ultrasonography is recommended at least every 3 months for 4 years.