Wilms Tumor (Nephroblastoma): Causes, Symptoms, Treatment and Prognosis — Overview, Diagnosis & Treatment Options | MyMedicPlus

Wilms tumour (nephroblastoma) is the most common malignant kidney tumour in children and the fourth most common paediatric solid cancer overall, accounting for approximately 95% of all renal tumours in children under 15 years of age. Approximately 500-600 new cases are diagnosed per year in the United States, with a peak incidence at ages 3-4 years. Wilms tumour rarely occurs after the age of 15, although adult Wilms tumour — characterised by slightly different biology and treatment challenges — is an established entity. The tumour is classified in five stages by the Children's Oncology Group (COG) and International Society of Paediatric Oncology (SIOPE/UMBRELLA) systems: Stage I (tumour confined to the kidney with intact capsule, completely resected), Stage II (tumour extends beyond the kidney, completely resected), Stage III (residual tumour confined to the abdomen — including positive margins, lymph node involvement, peritoneal spread, or tumour spillage), Stage IV (haematogenous metastases to lungs, liver, bone, or brain), and Stage V (bilateral Wilms tumour, present in 5-7% of cases). Histology is the other critical prognostic variable: favourable histology (FH) includes the classic triphasic nephroblastoma pattern and all subtypes without anaplasia; unfavourable histology (UH) is defined by the presence of anaplasia (focal or diffuse), which is associated with TP53 mutations and significantly inferior outcomes. Despite its classification as a malignancy, Wilms tumour is among the greatest success stories of paediatric oncology, with an overall 5-year survival rate exceeding 90% when treated at dedicated centres using risk-adapted protocols.

Wilms tumour arises from aberrant differentiation and persistent proliferation of metanephric blastema — the embryonic precursor tissue from which the kidney develops — rather than from a mutation in a differentiated renal cell. Nephrogenic rests (focal or diffuse, designated perilobar and intralobar) are developmentally arrested metanephric blastema found in the kidney adjacent to Wilms tumour and in the contralateral kidney in bilateral cases; they are the proposed precursor lesion. The molecular aetiology of Wilms tumour is heterogeneous. WT1 tumour suppressor gene mutations on chromosome 11p13 are present in approximately 10-15% of sporadic cases but in a substantially higher proportion of syndromic cases. WT2 (the genomic imprinting region at 11p15.5) dysregulation — including loss of imprinting and paternal isodisomy — drives Beckwith-Wiedemann syndrome (BWS)-associated Wilms tumour. Established hereditary predisposition syndromes with significantly elevated Wilms tumour risk include: WAGR syndrome (Wilms tumour, Aniridia, Genitourinary anomalies, intellectual disability — caused by constitutional 11p13 deletion encompassing WT1 and PAX6; lifetime Wilms tumour risk approximately 30-50%); Denys-Drash syndrome (WT1 missense mutation causing diffuse mesangial sclerosis with nephrotic syndrome, GU ambiguity, and near-universal Wilms tumour risk); Beckwith-Wiedemann syndrome (11p15 overgrowth syndrome, Wilms tumour risk approximately 7-10%); Perlman syndrome; DICER1 syndrome; and isolated hemihypertrophy (one-sided body overgrowth; Wilms tumour risk approximately 3-5%). The majority (approximately 85%) of Wilms tumours are sporadic without an identifiable germline predisposition. Bilateral Wilms tumour (Stage V) is almost always associated with hereditary predisposition and warrants germline genetic evaluation.

The most common and often the only presentation of Wilms tumour is a large, palpable, asymptomatic abdominal or flank mass, frequently discovered by parents during bathing or nappy changing or by a primary care physician during routine examination. Because the tumour arises from and expands within the renal capsule, it often achieves considerable size — sometimes occupying more than half the abdominal cavity — before producing symptoms. Distinguishing clinical features include the smooth, firm, non-tender nature of the mass and the fact that, unlike neuroblastoma, Wilms tumour characteristically does not cross the midline. Abdominal pain or discomfort occurs in approximately 30-40% of patients, often from rapid expansion, haemorrhage into the tumour, or stretching of the renal capsule. Gross haematuria (visible blood in the urine) occurs in approximately 20% of children but is less common as a presenting feature than in adult renal cell carcinoma. Hypertension, present in approximately 20-25% of cases, results from excess renin secretion by the tumour or from compression of the renal vasculature. Microscopic haematuria and proteinuria are detected on urinalysis in a significant proportion. Anaemia may result from haemorrhage into the tumour (acute haemoperitoneum from spontaneous rupture is rare but catastrophic) or from bone marrow suppression in advanced metastatic disease. Fever occurs in approximately 20% of patients. Rapid increase in abdominal girth from acute intratumoral haemorrhage may be the first presentation. Uncommon presentations include lung symptoms (cough, dyspnoea) from pulmonary metastases or varicocele from tumour thrombus in the renal vein extending into the inferior vena cava.

The diagnostic workup for Wilms tumour begins with abdominal ultrasound, the first-line imaging modality that confirms the intra-renal origin of the mass, assesses renal vein and IVC tumour thrombus extension, evaluates the contralateral kidney for synchronous lesions, and detects liver metastases. CT of the chest and abdomen with intravenous contrast is mandatory for pre-operative staging: it provides detailed assessment of tumour extent, local invasion, regional lymph nodes, and pulmonary metastases (present in approximately 10-12% of patients at diagnosis). MRI of the abdomen provides superior vascular anatomy and bilateral tumour delineation, particularly for bilateral (Stage V) Wilms tumours and when nephron-sparing surgery is planned, as it optimally delineates tumour margins from residual normal renal parenchyma. Tissue biopsy prior to surgery is not routinely performed in the North American (COG) approach for unilateral resectable Wilms tumour, as pre-operative tumour rupture from biopsy constitutes an upstaging event requiring abdominal irradiation; biopsy is performed for bilateral, unresectable, or atypical presentations before pre-operative chemotherapy in the SIOPE approach. Histological classification on the surgical specimen distinguishes favourable histology (FH, no anaplasia) from unfavourable histology (UH, focal or diffuse anaplasia). Molecular markers increasingly guide treatment stratification: 1q gain (found in approximately 20% of WTs) is associated with increased relapse risk even in FH tumours and is used by COG protocols to escalate therapy; 16q and 1p loss of heterozygosity (LOH) were historically used as UH-equivalent risk factors but have been supplanted by 1q gain in current protocols.

Two major international cooperative group protocols guide treatment: the North American Children's Oncology Group (COG) AREN1232 protocol and the European UMBRELLA SIOPE-RTSG protocol, which differ primarily in the timing of surgery relative to chemotherapy but achieve comparable excellent outcomes. COG approach: primary radical nephrectomy — complete removal of the affected kidney, adrenal gland, and regional lymph node sampling — is performed first without pre-operative chemotherapy, enabling definitive pathological staging and histological classification. Post-operative risk-adapted adjuvant chemotherapy is assigned based on stage and histology: Stage I-II FH: vincristine plus actinomycin D (EE4A, 18 weeks); Stage III-IV FH: add doxorubicin (DD4A, 24 weeks); Stage I-III FH with 1q gain: escalated to DD4A; Stage I-II UH: DD4A or regimen M (vincristine, actinomycin D, doxorubicin, cyclophosphamide, etoposide) based on anaplasia type; Stage III-IV diffuse anaplasia (DA): regimen M. Abdominal radiotherapy (10.8 Gy in 6 fractions) is given for Stage III disease (peritoneal spread, positive surgical margins, incomplete resection, ruptured tumour, lymph node involvement) and whole-lung radiotherapy (12 Gy) for persistent pulmonary metastases after 6 weeks of chemotherapy. SIOPE/UMBRELLA approach: 4 weeks of pre-operative vincristine plus actinomycin D before nephrectomy, potentially enabling nephron-sparing surgery in small tumours and reducing intraoperative tumour rupture risk in large tumours. Bilateral Wilms tumour (Stage V): pre-operative chemotherapy (vincristine-actinomycin D x 4-6 weeks) followed by bilateral nephron-sparing surgery is the universal approach, aiming to preserve maximum renal parenchyma in both kidneys to prevent end-stage renal disease; dialysis-requiring renal failure occurs in approximately 1% of unilateral but up to 10-15% of bilateral Wilms tumour survivors.

Primary prevention of sporadic Wilms tumour is not currently achievable given its embryonic origin and the poorly understood molecular triggers of metanephric blastema persistence. However, secondary prevention through structured surveillance in high-risk individuals — enabling detection of early-stage, highly curable tumours — is an evidence-based and clinically implemented strategy. Children with WAGR syndrome or aniridia at birth: renal ultrasound every 3 months from birth until age 8 years is recommended, as the 30-50% lifetime Wilms tumour risk and the tumour's rapid growth rate make frequent surveillance intervals necessary. Children with Beckwith-Wiedemann syndrome: abdominal ultrasound every 3 months from birth until age 8 years (Wilms tumour risk approximately 7-10%). Children with Denys-Drash syndrome: renal ultrasound every 3 months from birth; preventive nephrectomy of the most severely affected kidney may be discussed given the near-universal risk. Children with isolated hemihypertrophy: renal and liver ultrasound every 3 months until age 7-8 years. Children with DICER1 syndrome: annual abdominal imaging. All children with aniridia — even without known WAGR syndrome — should have renal ultrasound every 3 months until age 5 years, as aniridia is a strong clinical marker for WT1 deletion. Germline genetic testing is recommended for children with bilateral Wilms tumour, familial Wilms tumour, Wilms tumour with associated congenital anomalies, and nephrogenic rests in the contralateral kidney. Families with a confirmed hereditary predisposition syndrome should receive genetic counselling and surveillance planning at a specialist paediatric oncology centre.

Parents should seek urgent medical evaluation if they notice a palpable abdominal lump or abdominal swelling in their child, regardless of whether the child appears well or unwell — Wilms tumour is classically painless and may be very large without causing significant symptoms. Any abdominal mass in a child under 15 years of age must be evaluated with imaging (ultrasound, then CT) before any attempt at biopsy or surgical excision outside a specialist paediatric oncology centre, to avoid tumour rupture and inadvertent upstaging. Blood in the urine (visible haematuria) in a child of any age warrants urgent renal ultrasound to exclude an intra-renal mass. Unexplained hypertension in a child — particularly if associated with abdominal fullness or a palpable flank mass — requires renal imaging to exclude Wilms tumour. Children who are known to have WAGR syndrome, Beckwith-Wiedemann syndrome, hemihypertrophy, aniridia, Denys-Drash syndrome, or DICER1 syndrome must attend their scheduled renal ultrasound surveillance appointments every 3 months without delay, as even brief delays in tumour detection can result in stage advancement. Any parent who notices one side of their child's abdomen appearing larger than the other, or who notices an asymmetric bulge in the flank, should seek urgent paediatric assessment rather than adopting a 'wait and see' approach. Wilms tumour in older children (over 10 years) and adolescents is rare but possible, and the same criteria for evaluation apply — particularly if associated with haematuria, abdominal mass, or hypertension.

Wilms tumour is among the most curable paediatric cancers. Overall 4-year OS exceeds 90%. Stage I FH: 4-year OS approximately 99%. Stage IV FH (metastatic): approximately 86% with aggressive multimodal treatment. Diffuse anaplasia Stage IV: approximately 55-65%. Bilateral Wilms (Stage V): approximately 80% OS with nephron-sparing surgery and chemotherapy. Late effects of treatment — including radiation-induced scoliosis, gonadal dysfunction, second malignancies, and renal insufficiency — require long-term follow-up at dedicated childhood cancer survivor clinics. The prognosis for Wilms Tumor (Nephroblastoma): Causes, Symptoms, Treatment and Prognosis varies depending on severity at diagnosis, the patient's overall health, and how promptly treatment is initiated. With early diagnosis and appropriate management, many patients achieve good outcomes and maintain quality of life. Regular follow-up with healthcare providers is essential to monitor progress, adjust treatment as needed, and detect any complications early. Adherence to prescribed treatments and lifestyle modifications significantly improves long-term prognosis.