A 4-year-old boy from rural Maharashtra presents with his mother to the pediatric outpatient clinic with a 2-month history of abdominal distension and a palpable mass in the left flank. On examination, the mass is firm, non-tender, and confined to the abdomen. Hemoglobin is 9.2 g/dL. Abdominal ultrasound shows a large heterogeneous mass arising from the left kidney with areas of cystic change. CT abdomen confirms a 6 cm intrarenal mass with no evidence of distant metastases. Which of the following is the most appropriate next step in management?

Explanation

## Wilms Tumor: Neoadjuvant Chemotherapy Strategy ### Clinical Context This 4-year-old presents with a classic presentation of Wilms tumor: unilateral flank mass in early childhood with mild anemia and no evidence of metastatic disease at presentation. ### Standard Treatment Approach **Key Point:** The modern management of Wilms tumor (stages I–III) follows the COG (Children's Oncology Group) and SIOP (Société Internationale d'Oncologie Pédiatrique) protocols, which differ in timing of chemotherapy relative to surgery. **High-Yield:** The SIOP approach (used in many centers including India) recommends **preoperative (neoadjuvant) chemotherapy** for 4–6 weeks followed by surgical resection. This strategy: 1. Reduces tumor volume, facilitating safer surgical resection 2. Decreases operative morbidity and blood loss 3. Allows assessment of chemotherapy response 4. Improves overall survival in intermediate and high-risk tumors ### Why Neoadjuvant Chemotherapy? - Shrinks the tumor mass, reducing risk of tumor spillage during surgery - Allows assessment of histology (favorable vs. unfavorable) after chemotherapy response - Reduces need for extended resection of adjacent organs - Standard of care in most pediatric oncology centers globally **Clinical Pearl:** Chemotherapy agents used include vincristine, dactinomycin, and doxorubicin (VAD regimen). Response is assessed by imaging after 4 weeks. ### Staging and Prognosis | Stage | Definition | 5-year Survival | |-------|-----------|----------------| | I | Tumor confined to kidney, completely resected | >95% | | II | Tumor extends beyond kidney but completely resected | >90% | | III | Incomplete resection or regional nodal involvement | 80–85% | | IV | Hematogenous or lymphatic metastases | 50–70% | | V | Bilateral renal involvement | 60–70% | **Mnemonic for Wilms Tumor Risk Factors:** **WAGR** = Wilms tumor, Aniridia, Genitourinary anomalies, mental Retardation (now: intellectual disability). Also: Beckwith-Wiedemann, Denys-Drash syndromes. ### Management Algorithm ```mermaid flowchart TD A[Suspected Wilms Tumor]:::outcome --> B[Imaging: Ultrasound + CT/MRI]:::action B --> C{Metastases present?}:::decision C -->|Yes| D[Stage IV: Immediate chemotherapy]:::action C -->|No| E{Bilateral kidneys involved?}:::decision E -->|Yes| F[Stage V: Neoadjuvant chemotherapy]:::action E -->|No| G[Unilateral tumor]:::outcome G --> H[Neoadjuvant chemotherapy 4-6 weeks]:::action H --> I[Reassess with imaging]:::action I --> J[Radical nephrectomy + lymph node dissection]:::action J --> K[Adjuvant chemotherapy based on stage & histology]:::action K --> L[Long-term follow-up]:::outcome ``` ### Why NOT the Other Options - **Immediate surgery without chemotherapy:** Increases operative morbidity and risk of tumor spillage; not standard of care in SIOP protocol. - **Observation alone:** Wilms tumor is rapidly progressive; delays in treatment worsen prognosis. [cite:Park 26e Ch 13, Pediatric Oncology]