Relapsed Wilms Tumor Management and Outcomes in Canada: A Report From CYP-C

BACKGROUND: Wilms tumor (WT) is the most common pediatric renal tumor. While relapse of WT occurs in up to 15%, its management is not well characterized. We aimed to describe the Canadian experience in relapsed WT and the potential effect of surgical intervention as part of multimodal therapy on survival. METHODS: We identified a cohort of patients with relapsed WT between 2001 and 2020 from the Cancer in Young People in Canada program (CYP-C), a population-based surveillance program. Four-year event-free survival (EFS) and overall survival (OS) were estimated using the Kaplan-Meier method. The effect of surgical intervention on 4-year EFS/OS was evaluated through a Cox proportional hazards model (which included the number of upfront chemotherapy drugs). RESULTS: Ninety-seven patients were identified. Median age at relapse was 5.2 years (range: 0.4 to 16.0) and median time to relapse from initial diagnosis was 13.0 months (range: 3.0 to 73.0). 28.9% of relapses occurred after initial upfront treatment with 2 chemotherapy drugs versus 62.9% with ≥3 drugs. Four-year EFS and OS from time of first relapse were 54.0% (95% CI: 44.6-65.4) and 61.6% (95% CI: 52.4-72.6), respectively. Seventy-one percent of patients with relapsed WT had surgery as part of multimodal therapy. The hazard ratio associated with surgical intervention in multiple regression was 0.54 for EFS (95% CI: 0.29-1.02; P =.06) and 0.36 for OS (95% CI: 0.19-0.71; P =.003). CONCLUSIONS: Outcomes compare favorably to those reported by international cooperative groups. More favorable survival was observed in patients amenable to surgical intervention at relapse. This association may reflect a true therapeutic benefit of resection or may be confounded by the extent of disease at presentation, response to chemotherapy, the patient's performance status, or other variables. The impact of these on outcomes should be further investigated.