NSS was only performed in 3% of patients with uWT. Despite excellent survival with few relapses, the gain of nephrons needs to be weighed against the risk to induce stage III with intensified therapy.

Outcome for children with MN is excellent at all ages, with little indication for adjuvant chemotherapy. Children presenting at <3 months of age, should be treated by primary nephrectomy. In those presenting aged >3 months, alternative diagnoses should be considered, especially in the presence of surgical risk factors.

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Introduction The International Society of Paediatric Oncology (SIOP) protocols recommend pre-operative chemotherapy appropriate for Wilms tumours (WT) in children with renal tumours aged ≥6 months, reserving biopsy for ‘atypical’ cases. The Children’s Cancer and Leukaemia Group (CCLG) joined the SIOP-WT-2001 study but continued the national practice of biopsy at presentation. Method Retrospective study of concordance between locally reported renal tumour biopsies and central pathology review nephrectomy diagnoses of children enrolled by CCLG centres in SIOP-WT-2001 Study. Results Biopsy reports were available for 552/787 children with unilateral tumours. 36/552 (6.5%) were non–diagnostic: 2 normal tissue, 12 necrotic, 9 insufficient sample and 13 indeterminate results (disproportionately non-WTs). The sensitivity and specificity of biopsy to identify tumours that did not require SIOP empirical pre-operative chemotherapy were 86.0% and 99.6%, respectively. 13/548 (2.4%) biopsy results were discordant with nephrectomy; non-WTs other than renal cell carcinoma and clear cell sarcoma (CCSK) were poorly recognised. In children aged 6-119 months, 480/518 (91.6%) had WT or nephroblastomatosis. 5/518 (1%) had benign tumours, only one diagnosed on biopsy. Biopsy results correctly changed clinical management in 25/518 (4.8%), including identifying 19/20 CCSKs, but would have led to overtreatment in 5/518 (1%) or undertreatment in 4/518 (0.8%). In children aged ≥10 years, biopsy correctly changed management in 5/19 (26%) cases with no discordance. Conclusion Biopsy is less effective at identifying non-WTs than WTs and rarely changes management in younger children. Biopsy should be reserved in SIOP protocols for children ≥10 years and in younger children with clinical or radiological features inconsistent with WT.

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