Characteristics and outcomes of preoperatively treated patients with anaplastic Wilms tumors registered in the UK SIOP-WT-2001 and IMPORT study cohorts (2002-2020).

Background: Since the International Society of Paediatric Oncology Wilms' Tumour 2001 (SIOP-WT-2001) study, focal anaplastic Wilms tumors (FAWTs) have been treated as intermediate-risk Wilms tumors (WTs), and diffuse anaplastic Wilms tumors (DAWTs) have been treated as high-risk tumors.

Methods: The authors performed a retrospective analysis of preoperatively treated patients with FAWT or DAWT recruited in 2 consecutive UK Children's Cancer and Leukaemia Group WT studies.

Results: One hundred twenty-one of 1237 patients (10%) had an anaplastic WT confirmed by central pathology review (CPR): 93 (77%) had DAWT, and 28 (23%) had FAWT. The 4-year event-free survival (EFS) was 51% (95% confidence interval [CI], 41%-63%) for DAWT, 88% (95% CI, 76%-100%) for FAWT, and 84% (95% CI, 82%-87%) for intermediate-risk nonanaplastic Wilms tumor (IR-non-AWT). Overall survival (OS) was 58% (95% CI, 48%-70%) for DAWT, 95% (95% CI, 86%-100%) for FAWT, and 95% (95% CI, 93%-96%) for IR-non-AWT. In a multivariate analysis, the presence of DAWT was a significant prognostic factor for both EFS and OS in stages II, III, and IV. In a multivariate analysis of unilateral DAWT, stages III and IV remained the only significant prognostic factors for both EFS and OS. In 28% of the cases, there were discrepancies affecting the recognition of anaplasia, classification (DAWT vs FAWT), or the local pathologic stage.

Conclusions: Preoperatively treated patients with FAWT had excellent outcomes in comparison with those with identically treated IR-non-AWT, whereas patients with DAWT showed significantly worse outcomes. All patients with stage I disease had comparable good outcomes, regardless of the presence/absence of anaplasia. In contrast, the presence of DAWT was associated with significantly worse outcomes for patients with stage II to V disease. Finally, significant diagnostic discrepancies emphasize the value of CPR.

Lay Summary: Anaplasia is an unfavorable feature in Wilms tumor (WT), and it is classified as focal (focal anaplastic Wilms tumor [FAWT]) or diffuse (diffuse anaplastic Wilms tumor [DAWT]). This study reports the outcomes of patients with FAWT and DAWT who were, for the first time, treated differently. Patients with FAWT received less intensive treatment, and their outcomes were comparable to the outcomes of patients with identically treated nonanaplastic WT. Patients with stage I DAWT also had good outcomes when they were treated without radiotherapy, whereas patients with stage II to V DAWT had poor outcomes despite more intensive treatment.