nephroblastoma

Nephroblastoma (Wilms tumor) is derived from primitive metanephric blastema and classically shows a triphasic histology consisting of blastemal, stromal, and epithelial elements, recapitulating normal renal development. It typically presents as a large, unilateral, smooth abdominal/flank mass in a child, often discovered incidentally by a parent or on exam, and may be accompanied by hematuria, hypertension (due to renin secretion), and abdominal pain. It is the most common renal tumor of childhood, with peak incidence between 2-5 years of age.

Genetics: Associated with mutations/deletions in WT1 tumor suppressor gene on chromosome 11p13. Wilms tumor is a component of several syndromes: - WAGR syndrome: Wilms tumor, Aniridia, Genitourinary anomalies, mental Retardation (11p13 deletion involving WT1 and PAX6) - Denys-Drash syndrome: Wilms tumor, early-onset nephropathy, male pseudohermaphroditism (WT1 mutation) - Beckwith-Wiedemann syndrome: macroglossia, organomegaly, hemihypertrophy, omphalocele (WT2 gene, 11p15)

Workup includes abdominal ultrasound and CT/MRI to assess for tumor extent, vascular invasion (renal vein/IVC), and metastases (most commonly to lungs). Bilateral involvement occurs in ~5-10% of cases.

Management: Nephrectomy combined with chemotherapy (vincristine, dactinomycin, +/- doxorubicin) and radiation for higher-stage disease. Prognosis is generally excellent, with >90% survival for favorable histology.

Histologic distinction: Favorable histology has better prognosis; anaplastic (unfavorable) histology with diffuse anaplasia carries worse prognosis. Must be differentiated clinically and radiographically from neuroblastoma, which arises from adrenal medulla/sympathetic chain, crosses midline, and is associated with elevated catecholamines (VMA/HVA), unlike Wilms tumor which does not cross midline and lacks catecholamine elevation.