American Urological Association - Malignant Rhabdoid Tumor
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Malignant Rhabdoid Tumor

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  • Age: generally <1 yr.; rarely over 3 years.
  • Inactivation of HSNF/INI1 tumor suppressor gene located at chr 22q11.2.
  • Majority presents with abdominal mass.
  • Paraneoplastic hypercalcemia from production of parathyroid hormone.
  • Gross: large yellow-gray or light tan friable tumor with infiltrative borders (image A).
  • Histology:
    • Large polygonal cells with abundant eosinophilic cytoplasm and large nuclei with prominent nucleoli.
    • Cytoplasm typically contains large round eosinophilic inclusions that push the nucleus to the side of the cell (image B).
    • Appearance simulates primitive skeletal muscle (hence the name "rhabdoid") - however this is an epithelial tumor and does NOT stain for skeletal muscle differentiation (desmin, muscle specific actin, etc.).
  • Immunohistochemistry: INI1-, surrogate marker of hSNF5/INI1 gene deletion.
  • Majority present with high stage tumor.
  • Extremely aggressive; death from metastatic disease occurs within 12 months in 75% of patients.