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Nephroblastoma (Wilms' Tumor)

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  • Constitute ~85% of childhood renal cancers.
  • Age: 2-4 years; extremely uncommon in children <6 months and >6 years.
  • Associations: WAGR syndrome, Beckwith-Wiedemann syndrome, and Denys-Drash syndrome.
  • Mostly presents as abdominal mass. (Detected by parents).
  • Bilateral in 5% of cases.
  • Radiology: calcification is uncommon (vs. neuroblastoma, which is often calcified).
  • Gross:
    • Usually large with solid soft gray tan cut surface and seemingly well-circumscribed borders (image A).
    • Hemorrhage and necrosis are common.

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  • Microscopic: 3 distinct elements:
    • Blastema: sheets of densely packed primitive small cells with scant cytoplasm and darkly staining nuclei ("small round blue cell tumor") (image B) & (image C).
    • Epithelial: small tubules or cysts lined by primitive or mature columnar or cuboidal cells.
    • Stroma: spindle cells or may differentiate along the lines of any soft tissue such as fibroblasts, smooth muscles or skeletal muscles, cartilage (image D); loose myxoid and fibroblastic spindle cell stromas are the most common.
    • Most tumors though have biphasic or monophasic growth.
  • Immunohistochemistry: WT1+ in blastemal and epithelial components.
  • Overall survival is good (>90%).
  • Unfavorable prognostic factors are high stage and presence of diffuse anaplasia.
  • DDX:
    • Other small round blue cell tumors including neuroblastoma (WT1-).