Malignant rhabdoid tumor

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]Associate Editor(s)-in-Chief: Sujit Routray, M.D. [2]

Synonyms and keywords: Malignant rhabdoid tumour; Malignant rhabdoid neoplasm; Atypical teratoid rhabdoid tumor

Overview

• Malignant rhabdoid tumor is one of the aggressive tumors in the pediatric population. It was originally described as a rhabdomyosarcomatoid variant of Wilms' tumor, which is primarily a renal tumor.
• Malignant rhabdoid tumor was first described as a variant of Wilms' tumor of the kidney, in 1978.
• Malignant rhabdoid tumor is classified into two groups: renal and extrarenal.
• Malignant rhabdoid tumor is comprised of rhabdoid tumor cells and varying amounts of small undifferentiated primitive neuroectodermal tumor (PNET)-like, mesenchymally, and/or epithelially differentiated tumor cells.
• Gene involved in the pathogenesis of malignant rhabdoid tumor include SMARCB1 (hSNF5/INI-1), a tumor suppressor gene.
• Malignant rhabdoid tumor is characterized by loss of the long arm of chromosome 22, which results in loss of the hSNF5/INI-1 gene.
• INI1, a member of the SWI/SNF chromatin remodeling complex, is important in maintenance of the mitotic spindle and cell cycle control.
• Malignant rhabdoid tumor may be associated with rhabdoid predisposition syndrome.
• Common locations associated with malignant rhabdoid tumor include:

• Kidney: malignant rhabdoid tumor of the kidney (most common)
• Intracranial: atypical teratoid rhabdoid tumor
• Soft tissues: breast, skin, orbit, liver, etc

• On gross pathology, malignant rhabdoid tumor of the kidney is characterized by large, centrally located, heterogeneous soft-tissue masses involving the renal hilum with indistinct margins.
• On microscopic histopathological analysis, malignant rhabdoid tumor is characterized by the round blue tumor cells of high cellularity composed of atypical cells with eccentric nuclei, small nucleoli, and abundant amounts of eosinophilic cytoplasm with frequent mitotic figures.
• Malignant rhabdoid tumor is demonstrated by positivity to tumor markers such as vimentin, EMA, AE1/AE3, and CAM5.2.
• Renal malignant rhabdoid tumor must be differentiated from renal cell carcinoma, Wilms' tumor, mesonephric nephroma, and primitive neuroectodermal tumor of the kidney.
• Extrarenal malignant rhabdoid tumor must be differentiated from desmoplastic small round cell tumor, rhabdomyosarcoma, and other soft tissue tumors.
• Almost all reported cases of malignant rhabdoid tumor, regardless of site of origin, occur in young children between birth and 2 years of age.
• In approximately 10% of cases of renal malignant rhabdoid tumor, the patients subsequently develop intracranial atypical teratoid rhabdoid tumor.
• Common complication of malignant rhabdoid tumor include hypercalcemia, secondary to elevated parathyroid hormone levels.
• Prognosis is generally poor, with a reported mortality rate of patients with malignant rhabdoid tumor is 80 to 100%.
• According to the Children’s Oncology Group (COG) staging system, there are 5 stages of malignant rhabdoid tumor.

Staging	Characteristic findings
Stage I	Iso- to hypointense solid component compared to adjacent brain
Stage II	Hyperintense solid component compared to adjacent brain
Stage III	Hyperintense solid component compared to adjacent brain
Stage IV	Hyperintense solid component compared to adjacent brain
Stage V	Hyperintense solid component compared to adjacent brain

• Symptoms of malignant rhabdoid tumor of kidney include:

• Blood in urine
• Flank mass

• Laboratory findings consistent with the diagnosis of malignant rhabdoid tumor include:

• Complete blood count: Reduced hemoglobin
• Liver function test: Elevated liver enzymes
• Urinalysis: Microscopic hematuria
• Serum calcium measurement: Elevated serus calcium (hypercalcemia)

• CT scan may be diagnostic of malignant rhabdoid tumor. Findings on CT scan suggestive of malignant rhabdoid tumor include a large, heterogenous, centrally located mass, which is lobulated with individual lobules separated by intervening areas of decreased attenuation, relating to either previous hemorrhage or necrosis. Enhancement is similarly heterogeneous. Calcification is relatively common, observed in 20-50% of cases and is typically linear and tends to outline tumur lobules.