Stage I epithelial or stromal type Wilms tumors are low risk tumors: An analysis of patients treated on the SIOP‐WT‐2001 protocol in the UK‐CCLG and GPOH studies (2001–2020)

Background Patients treated with preoperative chemotherapy with stage I intermediate‐risk Wilms tumor (IR‐WT) represent the largest group of patients with Wilms tumor (WT), and they have excellent outcomes. Methods The authors performed a retrospective analysis of patients with stage I epithelial (ET‐WT) or stromal type WT (ST‐WT) treated pre‐ and postoperatively according to the International Society of Paediatric Oncology‐WT‐2001 protocol in the UK Children's Cancer and Leukaemia Group and Gesellschaft für Pädiatrische Onkologie und Hämatologie groups' participation in the relevant WT trials and studies (2001–2020). Results There were 880 patients with stage I IR‐WT, including 124 with ET‐WT, 156 with ST‐WT, and 600 with other IR‐WT (oIR‐WT). Patients with stage I ET‐WT or ST‐WT were significantly younger than patients with oIR‐WT, represented a large proportion of stage I WTs in their groups, and tumors showed poor histologic response to preoperative chemotherapy. The 5‐year event‐free survival (EFS) estimates for patients with stage I ET‐WT (96.8% ± 1.8 SE) or ST‐WT (96.8% ± 1.6 SE) were significantly better than for patients with oIR‐WT (90.3% ± 1.3 SE) (p = .014 and p = .009, respectively). A multivariate analysis showed that histologic type (ET‐WT or ST‐WT) remained a significant factor for EFS when adjusted for age and gender (p = .032 and p = .022, respectively). In both groups, relapses occurred in 3.2% of patients, and the overall survival was 99.2%. Conclusions The results suggest that stage I ET‐WT or ST‐WT could be regarded as low‐risk WT, for which omission of postoperative chemotherapy should be considered. Plain Language Summary Patients with pretreated intermediate‐risk Wilms tumor (WT) represent the largest group of patients with WT. This study reports the outcomes of patients with stage I epithelial type (ET‐WT) or stromal type WT (ST‐WT). These patients were significantly younger and had a larger proportion of stage I cases than patients with other intermediate‐risk WT (oIR‐WT). The event‐free survival for patients with stage I ET‐WT and ST‐WT was significantly better than for patients with oIR‐WT. Rare relapses were curable resulting in 99.2% overall survival. Patients with stage I epithelial or stromal type Wilms tumor showed significantly better event‐free survival than patients with other stage I intermediate‐risk Wilms tumors. Rare relapses were curable resulting in nearly 100% overall survival.