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).
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.