Ultrasound-Based Monitoring in Unilateral Wilms Tumor: Treatment Response Assessment and Early Relapse Dynamics (2012–2020, Single-Center Cohort)

Background: Ultrasound-first (US-first) monitoring is commonly used in resource-variable settings to reduce radiation exposure; however, the prognostic value of neoadjuvant ultrasound response in unilateral Wilms tumor is not well defined in real-world cohorts. We assessed whether a simple dichotomized ultrasound response (regression vs non-regression) can stratify relapse and survival risk in children treated under SIOP principles. Methods: This retrospective single-center cohort included consecutive patients aged 0–18 years with unilateral Wilms tumor treated with SIOP-based protocols between 2012 and 2020 at the National Center of Oncology, Baku, Azerbaijan (n=59). Neoadjuvant response was assessed by abdominal ultrasonography using the largest axial tumor diameter and categorized as regression, stable disease, or progression (chemoresistance). For primary analyses, response was dichotomized as regression vs non-regression (stable+progression). Outcomes were relapse, overall survival (OS), and disease-free survival (DFS). Survival was estimated by the Kaplan–Meier method, and hazard ratios (HRs) were estimated using Cox regression. Results: Neoadjuvant USM response was regression in 50/59 (84.7%), stable disease in 5/59 (8.5%), and progression/chemoresistance in 4/59 (6.8%). Non-regression occurred only in stage III–IV disease (p=0.038). Over a median follow-up of 94 months, relapse occurred in 11/59 (18.6%) and death in 7/59 (11.9%); 81.8% of relapses occurred within 24 months. Relapse and death were markedly higher in the non-regression group than in the regression group (relapse 66.7% vs 10.0%; death 55.6% vs 4.0%; both p<0.001). At 60 months, OS was 96.0% vs 44.4% (p<0.001) and DFS was 90.0% vs 33.3% (p<0.001) for regression vs non-regression, respectively. In univariable Cox models, non-regression was strongly associated with worse outcomes (OS HR 16.89, 95% CI 3.27–87.20, p<0.001; DFS HR 8.90, 95% CI 2.70–29.36, p<0.001). Conclusions: In this real-world SIOP-treated unilateral Wilms tumor cohort, a simple US-first neoadjuvant response classification strongly stratified relapse and long-term survival risk. Ultrasound non-regression identifies a high-risk subgroup that may warrant closer early monitoring in radiation-sparing follow-up strategies.