Evaluation of boost irradiation in patients with intermediate-risk stage III Wilms tumour with positive lymph nodes only : Results from the SIOP-WT-2001 Registry

Objective: To evaluate the value of radiotherapy boost omission in patients with intermediate‐risk, stage III Wilms tumours (WT) with positive lymph nodes (LN). Methods and materials: All patients with intermediate‐risk, stage III (LN positive) WT consecutively registered in the SIOP‐WT‐2001 study were included in this analysis. Endpoints were 5‐year event‐free survival (EFS), loco‐regional control (LRC) and overall survival (OS). Results: Between June 2001 and May 2015, 2,569 patients with stage I to III WT after preoperative chemotherapy were registered in the SIOP‐WT‐2001 study. Five hundred and twenty‐three (20%) had stage III disease, of which 113 patients had stage III due to positive LN only. Of those, 101 (89%) received radiotherapy, 36 of which (36%) received, apart from flank irradiation, a boost dose to the LN positive area. Four patients (4%) did not receive any adjuvant radiotherapy. In eight patients information on radiotherapy was not available. With a median follow‐up of 71 months, no difference in 5‐year EFS (84% vs. 83%, P = 0.77) and LRC (96% vs. 97%, P = 0.91) was observed between patients receiving a radiotherapy boost and those without boost, respectively. Five‐year OS, including salvage therapy, was excellent (boost vs. no boost: 97% vs. 95%, P = 0.58). Conclusions: Outcome data demonstrate that omission of the radiotherapy boost to the loco‐regional positive lymph nodes in patients with intermediate‐risk, stage III WT who receive preoperative chemotherapy and postoperative flank irradiation (14.4 Gy) can be considered a safe approach for future SIOP protocols.