A 4-year-old boy presents with a unilateral abdominal mass, hematuria, and hypertension. Imaging confirms a Stage III Wilms tumor with favorable histology. Which drug is the cornerstone of the chemotherapy regimen for this patient?

Explanation

## First-Line Chemotherapy for Wilms Tumor **Key Point:** Dactinomycin is the cornerstone agent in all Wilms tumor chemotherapy regimens, regardless of stage or histology. ### Standard Wilms Tumor Chemotherapy Regimens The most commonly used regimens are: | Regimen | Drugs | Indication | |---------|-------|-------------| | **VA** | Vincristine + Dactinomycin | Low-risk, favorable histology, Stage I–II | | **VAD** | Vincristine + Dactinomycin + Doxorubicin | Intermediate-risk, Stage III–IV, unfavorable histology | | **VAID** | Vincristine + Dactinomycin + Ifosfamide + Doxorubicin | High-risk, anaplastic, diffuse hyperplasia | **High-Yield:** Dactinomycin is present in EVERY Wilms tumor chemotherapy protocol. It is an actinomycin (intercalating agent) that is highly effective in pediatric malignancies. ### Why Dactinomycin Is Essential 1. **Proven efficacy** — Part of the original successful COG (Children's Oncology Group) protocols that transformed Wilms tumor survival from <10% to >90%. 2. **Synergy with vincristine** — The VA backbone is the foundation of all modern Wilms protocols. 3. **Favorable toxicity profile in children** — Compared to platinum agents, dactinomycin is better tolerated in the pediatric population. 4. **Intercalating mechanism** — Binds DNA and inhibits transcription, particularly effective in embryonal tumors. **Clinical Pearl:** In this patient with Stage III favorable-histology Wilms tumor, the regimen would be **VAD** (vincristine + dactinomycin + doxorubicin), typically given preoperatively (neoadjuvant) followed by surgery and postoperative chemotherapy. **Warning:** Do not confuse with neuroblastoma, which uses different agents (cyclophosphamide, doxorubicin, cisplatin, etoposide, topotecan).