A 3-year-old boy from rural Maharashtra presents with a painless abdominal mass noticed by his mother during bathing. On examination, the mass is firm, non-tender, confined to one side of the abdomen, and does not cross the midline. Vital signs are normal. Hemoglobin is 10.2 g/dL. Abdominal ultrasound shows a large heterogeneous mass arising from the left kidney with no evidence of distant metastases on chest X-ray. What is the most appropriate next step in management?

Explanation

## Management Algorithm for Wilms Tumor **Key Point:** Wilms tumor management follows a risk-stratified, multimodal approach. Staging with imaging (CT/MRI) and risk assessment precedes definitive surgery and chemotherapy. ### Diagnostic and Staging Workup Once Wilms tumor is suspected clinically and on ultrasound: 1. **Contrast-enhanced imaging** (CT abdomen/pelvis ± chest CT) is mandatory to: - Assess tumor size, local invasion, and renal vein/IVC involvement - Detect contralateral renal involvement (5–10% of cases) - Identify distant metastases (lungs, liver, lymph nodes) - Guide staging (Stage I–V per COG/SIOP) 2. **Risk stratification** based on: - Tumor histology (favorable vs. unfavorable) - Stage at diagnosis - Age and tumor size 3. **Treatment pathway** depends on risk: - **Low/intermediate risk:** Upfront nephrectomy followed by adjuvant chemotherapy - **High risk or bilateral disease:** Neoadjuvant chemotherapy (4–6 weeks) to reduce tumor burden, then delayed nephrectomy **High-Yield:** The COG (Children's Oncology Group) and SIOP (Société Internationale d'Oncologie Pédiatrique) protocols both mandate imaging staging before surgery. Neoadjuvant chemotherapy is used selectively in advanced/high-risk cases to improve surgical outcomes and reduce morbidity. **Clinical Pearl:** In this case, the child has a unilateral, non-metastatic tumor with normal vital signs—likely intermediate risk. Staging CT will determine whether upfront surgery or neoadjuvant therapy is appropriate. ### Why Immediate Surgery Is Premature - **Incomplete staging** risks inadequate treatment planning - **Tumor thrombus** (renal vein/IVC) may not be evident on ultrasound alone - **Contralateral involvement** must be excluded before unilateral nephrectomy - **Risk stratification** cannot occur without histology and stage ### Why Biopsy Is Not Standard - Percutaneous biopsy carries risk of tumor spillage and peritoneal seeding - Histology is obtained from the nephrectomy specimen - Imaging + clinical presentation is sufficient for presumptive diagnosis in this age group ```mermaid flowchart TD A[Suspected Wilms Tumor<br/>Clinical + Ultrasound]:::outcome --> B[Contrast-Enhanced CT<br/>Abdomen/Pelvis/Chest]:::action B --> C{Risk Stratification<br/>Stage + Histology}:::decision C -->|Low/Intermediate<br/>Unilateral| D[Upfront Nephrectomy]:::action C -->|High Risk or<br/>Bilateral| E[Neoadjuvant Chemotherapy<br/>4-6 weeks]:::action D --> F[Adjuvant Chemotherapy<br/>± Radiation]:::action E --> G[Delayed Nephrectomy]:::action G --> F F --> H[Surveillance]:::outcome ``` **Citation:** [cite:Park 26e Ch Pediatric Malignancies]