Outcomes of patients with Wilms' tumour stage III due to positive resection margins only: An analysis of patients treated on the SIOP‐WT‐2001 protocol in the UK‐CCLG and GPOH studies

Stage III Wilms' tumour (WT) represents a heterogeneous group which includes different criteria, but all stage III patients are treated according to the same study regiment. The aim of the study was to retrospectively analyse outcomes in patients with stage III due to positive resection margins (RM) only, sub‐grouped in RM with viable (RM‐v) and nonviable (RM‐nv) tumour. Patients were treated pre‐ and postoperatively according to the SIOP‐WT‐2001 protocol in the UK‐CCLG and GPOH WT trials and studies (2001‐2020). There were 197 patients, including 134 with localised, abdominal stage III and 63 with overall stage IV, but abdominal stage III. Stage III due to RM‐v had 126 patients, and due to RM‐nv 71 patients. The overall 5‐year local‐relapse‐free survival (RFS), event‐free (EFS) and overall survival (OS) estimates for all patients with abdominal stage III RM were 95.7% (±SE1.5%), 85.1 (±SE2.6%) and 90.3% (±SE2.2%), respectively. Patients with stage III RM‐nv had significantly better RFS and EFS than patients with RM‐v (P = .027 and P = .003, respectively). A multivariate analysis showed that RM‐v remained a significant factor for EFS when adjusted for age, presence of metastasis at diagnosis, histological risk group and overall stage in Cox regression analysis (P = .006). Patients with stage III due to RM‐nv only exhibited no local recurrence and have a significantly better RFS and EFS than patients with RM‐v. The results suggest that exclusion of RM‐nv as a stage III criterion in the UMBRELLA staging system and consequent treatment reduction is warranted. What's new? Criterion for abdominal stage III Wilms' tumour with positive resection margins is based on the finding of resection margin viable tumour (RM‐v) or by evidence of chemotherapy‐induced changes (CIC) at the resection margin (RM‐nv). Previous studies indicate that RM‐nv can be ignored for staging in different clinical situations. Here, comparison of outcomes among stage III Wilms' tumour patients staged by RM‐v vs RM‐nv shows that RM‐nv patients fare better in terms of local‐relapse‐free and event‐free survival compared to RM‐v patients. Moreover, RM‐nv patients experienced no local recurrence. Thus, RM‐nv can be ignored as a stage III criterion, reducing patient treatment.