• The tumor at the time of discovery was too massive to surgically remove. The patient was treated with chemotherapy first. The tumor reduced in size and was removed.

• Note the fibrous rim (arrow) that demarcates the tumor from the uninvolved kidney.

• The gross features suggest that the tumor originated from the peripheral renal parenchyma.

•Evidence is strong for a genetic/developmental etiology.

•The tumor may arise as a result of failure of blastemal tissue to differentiate into normal renal structures.

•Occurs in children, usually under age 5.

•Peak incidence between ages 1 and 3.

•Occurs in approximately 7 in a million children per year in the U.S.

•Occurs as part of WARG syndrome (Wilms tumor, aniridia, retardation, genital abnormalities).

•Occurs as part of Denys-Drash syndrome (gonadal dysgenesis and nephropathy leading to renal failure).

•Occurs as part of Beckwith-Wiedemann syndrome (organomegaly, hemihypertrophy, renal cysts, adrenal cytomegaly).

•The clinical presentation is that of a large abdominal mass in a child, usually 1 to 5 years old.

•The neoplasm is aggressive and metastasizes widely, but is responsive to combination therapy.
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•At the time of detection, Wilms tumors are usually large and dwarfs the native kidney.

•The cut surface is usually soft, fleshy and brain-like.

•Irregular areas of hemorrhage and necrosis may be present.

•The classic Wilms tumor is triphasic showing areas that are blastemal (non-descript undifferentiated small round cells), areas that show epithelial differentiation (tubules, glomeruloid structures) and areas that show stromal differentiation (spindle shaped cells, skeletal muscle).

•Mitotic figures are usually plentiful.

• Cotran RS, Kumar V, Robbins SL: Robbins Pathologic Basis of Disease. 5th ed. Philadelphia, W.B. Saunders, 1994, pp. 462-464.

• Current literature from PubMed at National Library of Medicine