Rhadoid tumor is composed of a diffuse proliferation of rounded to polygonal cells with eccentric nuclei and glassy eosinophilic cytoplasm containing hyaline-like inclusion bodies.
Scattered cells contain clearly evident cytoplasmic round structures. There are many mitoses.
Because rhabdoid features are focally observed in a wide variety of malignant tumors, including soft-tissue sarcomas, carcinomas, and meningiomas, investigators have debated whether or not these tumors arising within soft tissue are actually a specific diagnostic entity or simply a poorly differentiated neoplasm with a rhabdoid phenotype.
Renal malignant rhabdoid tumor was historically classified as a rhabdomyosarcomatoid variant of Wilms tumor, this tumor is now recognized as an entity separate from a Wilms tumor. MRT differs from Wilms tumor in that it exhibits early local and distant metastases and resistance to chemotherapy. The overall survival rate for Wilms tumors exceeds 85%, whereas the survival rate for MRT is only 20-25%. Malignant rhabdoid tumors have been reported in practically every location in the body, including the brain, liver, soft tissues, lung, skin, and heart (Geller).
Further complicating this issue is the molecular finding of the hSNF5/INI1 (a.k.a SMARCB1) gene in both extra-renal rhabdoid tumors and proximal epithelioid sarcoma (Modena). The deletion of the long arm of chromosome 22 (22q11.2) is a recurrent genetic characteristic.
Rhabdoid tumors usually co-express vimentin and epithelial markers. Despite resemblance to rhabdomyosarcoma, muscle markers are not expressed.
Usually arise in young children (median age of diagnosis is 13 months). This tumor is rare in children over 5 years old. In comparison, the median age of diagnosis for Wilms tumor is 3 years of age.
20% of patients may have hypercalcemia.
Malignant rhabdoid tumors frequently contain deletions at chromosome locus 22q11.1. This locus contains the SMARCB1 gene, also known as the hSNF5 or INI1 gene.
Despite aggressive chemotherapy, these tumors are usually rapidly fatal. They are widely metastatic, especially to the CNS.
Geller J. Malignant rhabdoid tumor. Last updated on Dec 2009. Available at: emedicine.medscape.com/article/993084-overview
Modena P, Lualdi E, Facchinetti F et al. SMARCB1/INI1 tumor suppressor gene is frequently inactivated in epithelioid sarcomas. Cancer Res 2005; 65: 4012–19.