atypical teratoid/rhabdoid tumor
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Definition: The atypical teratoid/rhabdoid tumour (AT/RT) is an uncommon tumour of the central nervous system in children, characterized by the presence of a rhabdoid cell component associated with variable combinations of primitive neuroectodermal tumour, mesenchymal and epithelial differentiation.
AT/RTs are rare, highly malignant embryonal CNS tumors, presenting mainly in very young children.They poorly respond to conventional adjuvant therapy protocols, but recent studies have shown that improved patient survival can be achieved with intensified aggressive therapy.
According to the current WHO classification, diagnosis of AT/RT is based on morphologic criteria that is, the presence of rhabdoid tumor cells.
Additionally, variable areas of primitive neuroectodermal and mesenchymal and/or epithelial differentiated tumor cells may be present.
Immunohistochemically, rhabdoid tumor cells almost always express epithelial membrane antigen (EMA) and vimentin, and to a variable extent smooth muscle actin , glial fibrillary acidic protein, neuronal antigens, and cytokeratin (CK).
Although immunohistochemical coexpression of mesenchymal and epithelial antigens is a characteristic feature, it is not absolutely specific for AT/RTs.
Differential diagnosis
Diagnosis of AT/RT may be difficult if characteristic rhabdoid features are not prominent and tumors are predominantly composed of small primitive cells, mesenchymal, and/or epithelial components.
Such cases may be misdiagnosed as supratentorial primitive neuroectodermal tumors (sPNETs), medulloblastomas, anaplastic ependymomas, choroid plexus carcinomas, glioblastomas, or malignant teratomas.
If AT/RT is suspected in such cases, cytogenetic and/or mutation analysis may be helpful.
Participants from a workshop on childhood AT/RTs agreed that the presence of an hSNF/INI1 gene mutation in a tumor with features suggestive of medulloblastoma or sPNET is sufficient to change the diagnosis to AT/RT, and treat the patients accordingly.
However, coding mutations can be detected only in approximately 75% of the rhabdoid tumors.
Also, cytogenetic studies in rhabdoid tumors are not always helpful, because other tumor entities with a complex karyotype may harbor monosomy 22 and in cases with uniparental disomy no deletions at chromosome 22q.11.2 are detectable by cytogenetic analysis.
Immunochemistry
no expression of hSNF5/INI1 (SMARCB1) (#15105654#) comparing with other CNS tumors of children
Comparative genomic hybridization (CGH)
losses from chromosome 22
associated 1p loss (#12787322#)
isolated 8p loss (#12787322#)
Differential diagnosis
medulloblastoma
References
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