A 2-year-old boy is incidentally found to have an abdominal mass on physical examination during a routine check. Ultrasound shows a large, well-circumscribed, intrarenal mass. CT confirms an 8 cm heterogeneous intrarenal mass with enhancing components. The contralateral kidney is normal. Which histological finding in this tumor is associated with worst prognosis?

• A Diffuse anaplasia (presence of multipolar mitotic figures) ✓
• B Blastemal predominant histology
• C Epithelial predominant histology
• D Stromal predominant histology

Explanation

Wilms tumor (nephroblastoma) is the most common renal malignancy in children, peaking at ages 3–4 years. Histologically, it contains blastemal, stromal, and epithelial components. Diffuse anaplasia is defined by the presence of giant polyploid nuclei, atypical (multipolar) mitotic figures, and nuclear enlargement ≥3x, and is associated with TP53 mutations. Diffuse anaplasia (particularly if focal anaplasia becomes diffuse) is the most important adverse histological risk factor, conferring significantly worse outcomes even with intensified therapy. Blastemal predominant histology in the post-treatment specimen (after neoadjuvant therapy per SIOP) indicates high risk. Epithelial and stromal predominant tumors have favorable histology.

Reference: Ghai Essential Pediatrics, 10th ed.

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Written and medically reviewed by the StethoPrep medical team.