Primary brain tumors, including atypical teratoid/rhabdoid tumors (AT/RTs), are a diverse group of diseases that together constitute the most common solid tumors of childhood. The PDQ childhood brain tumor treatment summaries are primarily organized according to the World Health Organization classification of nervous system tumors.[1,2] Brain tumors are classified according to histology, but immunohistochemical analysis, cytogenetic and molecular genetic findings, and measures of mitotic activity are increasingly used in tumor diagnosis and classification. Tumor location, extent of spread, and age at diagnosis are important factors that affect treatment and prognosis.[3-5] For a description of the classification of nervous system tumors and a link to the corresponding treatment summary for each type of brain tumor, see Childhood Brain and Spinal Cord Tumors Summary Index.
CNS AT/RT is a rare, clinically aggressive tumor that most often affects children aged 3 years and younger but can occur in older children and adults. Approximately one-half of AT/RTs arise in the posterior fossa.[6] The diagnostic evaluation includes magnetic resonance imaging (MRI) of the neuraxis and lumbar cerebrospinal fluid examination. AT/RT has been linked to somatic and germline variants of SMARCB1 and, less commonly, SMARCA4, both of which act as tumor suppressor genes.[7] There is no evidence-based standard treatment for children with AT/RT. Multimodality treatment consisting of surgery, chemotherapy (including high-dose chemotherapy), and radiation therapy is under evaluation in controlled clinical trials.
Based on current biological understanding, AT/RT is part of a larger family of rhabdoid tumors. In this summary, the term AT/RT refers to CNS tumors only, and the term rhabdoid tumor reflects the possibility of both CNS and non-CNS tumors. Unless specifically noted in the text, this summary refers to CNS AT/RT.
Childhood and adolescent cancer survivors require close monitoring because side effects of cancer therapy may persist or develop months or years after treatment. For specific information about the incidence, type, and monitoring of late effects in childhood and adolescent cancer survivors, see Late Effects of Treatment for Childhood Cancer.
The exact incidence of childhood CNS AT/RT is difficult to determine because the tumor is rare and has only been recognized since 1996.[8]
The incidence in older patients is unknown. However, in the Central Nervous System Atypical Teratoid/Rhabdoid Tumor Registry (AT/RT Registry), 12 of the 42 patients (29%) were older than 36 months at the time of diagnosis.[12]
Childhood AT/RT is a clinically aggressive tumor that primarily occurs in children younger than 3 years, but it also can occur in older children and adults.[13,14]
Approximately one-half of all AT/RTs arise in the posterior fossa, although they can occur anywhere in the CNS.[6,9] Tumors of the posterior fossa may occur in the cerebellopontine angle or more midline. Involvement of individual cranial nerves has been noted.[15]
Because AT/RTs grow rapidly, patients often have a fairly short history of progressive symptoms, measured in days to weeks. Signs and symptoms depend on tumor location. Young patients with posterior fossa tumors usually present with symptoms related to hydrocephalus, which include the following:
They may also develop ataxia, regression of motor skills, or localizing symptoms related to cranial nerve dysfunction.
Registry data suggest that 25% to 30% of patients present with disseminated disease.[5,12,16] Dissemination is typically through leptomeningeal pathways seeding the spine and other areas of the brain. Up to 35% of patients present with germline variants and may be prone to synchronous, multifocal tumors.[17-20]
All patients with suspected AT/RT should undergo MRI of the brain and spine. Unless medically contraindicated, the lumbar cerebrospinal fluid should be inspected for evidence of tumor. Patients may also undergo renal ultrasonography to detect synchronous tumors. Germline testing is also indicated.
AT/RTs cannot be reliably distinguished from other malignant brain tumors on the basis of clinical history or radiographic evaluation alone. Surgery is necessary to obtain tissue and confirm the diagnosis. Immunohistochemical staining for loss of SMARCB1 protein expression is also used to confirm the diagnosis.[21,22] Methylation array analysis has become an important adjunct to confirm the AT/RT subtype.[3,4]
Prognostic factors that affect survival for patients with AT/RTs are not fully delineated.
Known factors associated with a poor outcome include the following:
Most published data on outcomes of patients with AT/RT are from small series and are retrospective in nature. Initial retrospective studies reported an average survival from diagnosis of only about 12 months.[8,9,13,25,27] In a retrospective report, 2-year overall survival (OS) was better for patients who underwent a gross-total resection than for those who had a subtotal resection. However, in this study, the effect of radiation therapy on survival was less clear.[25]
There are reports of long-term survivors.[28] Notably, improved survival has been reported for those who received intensive multimodality therapy.[16,19]
Childhood central nervous system (CNS) atypical teratoid/rhabdoid tumor (AT/RT) was first described as a discrete clinical entity in 1987 [1] based on its distinctive pathological and genetic characteristics. Before then, it was most often classified as a medulloblastoma, CNS primitive neuroectodermal tumor (CNS PNET), or choroid plexus carcinoma. The World Health Organization (WHO) classifies AT/RT as an embryonal grade IV neoplasm.[2]
Histologically, AT/RT is morphologically heterogeneous, typically containing sheets of large epithelioid cells with abundant eosinophilic cytoplasm and scattered rhabdoid cells, most often with accompanying components of primitive neuroectodermal cells (small round blue cells), mesenchymal cells, and/or glial cells.[3]
Immunohistochemical staining for epithelial markers (cytokeratin or epithelial membrane antigen), glial fibrillary acidic protein, synaptophysin (or neurofilament), and smooth muscle (desmin) may help to identify the heterogeneity of differentiation, but will vary depending on the cellular composition.[4] Rhabdoid cells, while not present in all AT/RTs, will express vimentin, epithelial membrane antigen, and smooth muscle actin.
Immunohistochemical staining for the SMARCB1 protein is useful in establishing the diagnosis of AT/RT. A loss of SMARCB1 staining is noted in neoplastic cells, but staining is retained in non-neoplastic cells (e.g., vascular endothelial cells).[5-7]
AT/RT is a rapidly growing tumor that can have an MIB-1 labeling index of 50% to 100%.[8]
AT/RT was the first primary pediatric brain tumor in which a candidate tumor suppressor gene, SMARCB1, was identified.[9] SMARCB1 is genomically altered in most rhabdoid tumors, including CNS, renal, and extrarenal rhabdoid malignancies.[9] SMARCB1 is a component of the SWItch/Sucrose Non-Fermentable (SWI/SNF) chromatin-remodeling complex.[10]
Rare cases of rhabdoid tumors expressing SMARCB1 and lacking SMARCB1 variants have also been associated with somatic or germline variants of SMARCA4, another member of the SWI/SNF chromatin-remodeling complex.[7,11,12]
Less commonly, SMARCA4-negative (with retained SMARCB1) tumors have been described.[7,11,12] Loss of SMARCB1 or SMARCA4 staining is a defining marker for AT/RT.
The 2021 WHO classification defines AT/RT by the presence of either SMARCB1 or SMARCA4 alterations. Tumors with histological features of AT/RT that lack these genomic alterations are termed CNS embryonal tumors with rhabdoid features.[13]
Despite the absence of recurring genomic alterations beyond SMARCB1 and SMARCA4,[14-16] biologically, relatively distinctive subsets of AT/RT have been identified.[17-19] In one study, three distinctive subsets of AT/RT were identified through the use of DNA methylation arrays for 150 AT/RT tumors and gene expression arrays for 67 AT/RT tumors:[18]
In a subsequent study, the AT/RT SHH subgroup was further divided into three subtypes: SHH-1A, SHH-1B, and SHH-2.[22] Children older than 3 years who harbored the SHH-1B signature experienced the most favorable outcomes.
Loss of SMARCB1 or SMARCA4 protein expression has therapeutic significance, because this loss creates a dependence of the cancer cells on EZH2 activity.[23] Preclinical studies have shown that some AT/RT xenograft lines with SMARCB1 loss respond to EZH2 inhibitors with tumor growth inhibition and occasional tumor regression.[24,25] In a study of the EZH2 inhibitor tazemetostat, objective responses were observed in adult patients whose tumors had either SMARCB1 or SMARCA4 loss (non-CNS malignant rhabdoid tumors and epithelioid sarcoma).[26] For more information, see the Treatment of Recurrent Childhood CNS Atypical Teratoid/Rhabdoid Tumor section.
Cribriform neuroepithelial tumor has genomic and epigenomic characteristics that are very similar to those of AT/RT TYR.[20] The 2021 WHO Classification lists cribriform neuroepithelial tumor as a provisional entity. Like AT/RT, cribriform neuroepithelial tumor occurs in young children (median age, 1–2 years) and tumor cells lack SMARCB1 expression. Histologically, cribriform neuroepithelial tumor is characterized by the presence of cribriform strands and ribbons, but there is an absence of rhabdoid tumor cells with abundant eosinophilic cytoplasm. Like AT/RT TYR, tyrosinase expression is commonly observed. The outcome of patients with cribriform neuroepithelial tumor is more favorable than the outcome of patients with AT/RT TYR. In one study, only one death was reported among ten children with cribriform neuroepithelial tumor.[20]
RTPS, which is primarily related to germline SMARCB1 alterations (and less commonly to germline SMARCA4 alterations), has been clearly defined.[9,27] RTPS caused by SMARCB1 germline alterations is termed RTPS Type 1, while RTPS due to a SMARCA4 germline variant is called RTPS Type 2. RTPS is highly suggested in patients with synchronous occurrence of extracranial malignant rhabdoid tumor (kidney or soft tissue) and AT/RT, bilateral malignant rhabdoid tumors of the kidney, or malignant rhabdoid tumors in two or more siblings.
This syndrome is manifested by a marked predisposition to the development of malignant rhabdoid tumors in infancy and early childhood. Up to one-third of AT/RTs are thought to arise in the setting of RTPS, and most of these occur within the first year of life. The most common non-CNS malignancy of RTPS is malignant rhabdoid tumor of the kidney, which is also noted in infancy.[28,29]
A study of 65 children with rhabdoid tumors found that 23 (35%) had germline variants and/or deletions of SMARCB1.[5] Children with germline alterations in SMARCB1 presented at an earlier age than did sporadic cases (median age, approximately 5 months vs. 18 months) and were more likely to present with synchronous, multifocal tumors.[5] One parent was found to be a carrier of the SMARCB1 germline abnormality in 7 of 22 evaluated cases showing germline alterations, with four of the carrier parents being unaffected by SMARCB1-associated cancers.[5] This finding indicates that AT/RT shows an autosomal dominant inheritance pattern with incomplete penetrance.
Gonadal mosaicism has also been observed, as evidenced by families in which multiple siblings are affected by AT/RT and have identical SMARCB1 alterations, but both parents lack a SMARCB1 variant/deletion.[5,6] Screening for germline SMARCB1 variants in children diagnosed with AT/RT is suggested for counseling families on the genetic implications of their child’s AT/RT diagnosis.[5] Preliminary recommendations for the genetic evaluation and subsequent presymptomatic screening of nonaffected variant carriers (including parents and siblings of affected patients) have been reported and are likely to evolve as the understanding of RTPS improves.[28-30] In patients with a predisposition to AT/RT, whole-body magnetic resonance imaging may help to identify synchronous rhabdoid tumors outside of the CNS.
For more information about RTPS1 and SMARCB1, see Rhabdoid Tumor Predisposition Syndrome Type 1.
There is no evidence-based staging system for childhood central nervous system atypical teratoid/rhabdoid tumor. For treatment purposes, patients are classified as having newly diagnosed or recurrent disease, with or without neuraxis dissemination.
An evidence-based standard treatment for children with newly diagnosed central nervous system (CNS) atypical teratoid/rhabdoid tumor (AT/RT) has not yet been defined. Given the highly aggressive nature of the tumor, most patients have been treated with intensive multimodality therapy. However, the extent of treatment, particularly for radiation therapy, is limited because of the young age of most patients.
Treatment options for newly diagnosed CNS AT/RT include the following:
The extent of surgical resection may affect survival. Data from the Central Nervous System Atypical Teratoid/Rhabdoid Tumor Registry (AT/RT Registry) suggest that patients who have had a complete resection may have a longer median survival. However, complete surgical resection is often difficult because of the invasive nature of the tumor.[1]
Chemotherapy has been the main adjuvant therapy for very young children with AT/RT. Cooperative group studies that included children younger than 36 months demonstrated poor survival with standard chemotherapeutic regimens alone.[2] The Children’s Cancer Group reported a 2-year event-free survival (EFS) rate of 14% for 28 children younger than 36 months who were treated with multiagent chemotherapy.[3]
Intensive regimens that use varying combinations of high-dose chemotherapy,[4][Level of evidence C1]; [5,6][Level of evidence C2] intrathecal chemotherapy, and radiation therapy have led to prolonged survival for some patients.
Only two prospective trials for children with CNS AT/RT have been completed. In an institutional prospective trial, children were treated with a modified Intergroup Rhabdomyosarcoma Study-III (IRS-III) protocol, using intrathecal chemotherapy and radiation therapy. Of the subset of 20 children who completed therapy, the 2-year progression-free survival (PFS) rate was 53%, and the overall survival (OS) rate was 70%. Survival was better for patients who had a complete resection.[7][Level of evidence C1] In the Children's Oncology Group (COG) ACNS0333 (NCT00653068) study, patients were treated with intensive induction chemotherapy, followed by high-dose chemotherapy with autologous stem cell rescue and radiation therapy. The 4-year PFS rate was 37%, and the OS rate was 43%.[8][Level of evidence B4]
Thirteen patients in the AT/RT Registry were treated with high-dose chemotherapy with hematopoietic stem cell rescue as part of initial therapy.[1] Four of these patients, two of whom also received radiation, were alive without progressive disease 21.5 to 90 months after diagnosis at last report. Of 15 evaluable children (all younger than 32 months at diagnosis) who were on a chemotherapy Head Start III protocol, 2 survived for more than 47 months.[9][Level of evidence C1]
Radiation therapy appears to have a positive impact on survival for patients with AT/RT.[10]
Evidence (radiation therapy):
Evidence (multimodality therapy):
On the basis of the two prospective studies summarized above, multimodality therapy with surgery, radiation therapy, and chemotherapy seems to be the best treatment to optimize the survival of children with AT/RT. However, toxicities can be significant, and the most effective regimen and the optimal sequencing of therapies still need to be determined.
Early-phase therapeutic trials may be available for selected patients. These trials may be available via the Children’s Oncology Group, the Pediatric Brain Tumor Consortium, or other entities. Information about National Cancer Institute (NCI)–supported clinical trials can be found on the NCI website. For information about clinical trials sponsored by other organizations, see the ClinicalTrials.gov website.
There is no standard treatment for children with recurrent central nervous system (CNS) atypical teratoid/rhabdoid tumor (AT/RT).
Trials of molecularly targeted therapy are ongoing. In a study of the EZH2 inhibitor tazemetostat in adult patients with epithelioid sarcoma and non-CNS malignant rhabdoid tumors with SMARCB1 or SMARCA4 loss, prolonged stable disease and objective responses were observed.[1] In the National Cancer Institute (NCI)–Children's Oncology Group Pediatric MATCH APEC1621C (NCT03213665) trial, eight children with AT/RT received tazemetostat. One patient demonstrated disease stabilization.[2][Level of evidence B4]
Stereotactic radiation therapy/radiosurgery or focal radiation therapy can also be considered for the treatment of children with recurrent disease.[3]
Patients or families who desire additional disease-directed therapy should consider entering trials of novel therapeutic approaches because no standard agents have demonstrated clinically significant activity.
Regardless of whether a decision is made to pursue disease-directed therapy at the time of progression, palliative care remains a central focus of management. This ensures that quality of life is maximized while attempting to reduce symptoms and stress related to the terminal illness.
Early-phase therapeutic trials may be available for selected patients. These trials may be available via the Children’s Oncology Group (COG), the Pediatric Brain Tumor Consortium, or other entities. Information about National Cancer Institute (NCI)–supported clinical trials can be found on the NCI website. For information about clinical trials sponsored by other organizations, see the ClinicalTrials.gov website.
The following is an example of a national and/or institutional clinical trial that is currently being conducted:
Use our advanced clinical trial search to find NCI-supported cancer clinical trials that are now enrolling patients. The search can be narrowed by location of the trial, type of treatment, name of the drug, and other criteria. General information about clinical trials is also available.
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This PDQ cancer information summary for health professionals provides comprehensive, peer-reviewed, evidence-based information about the treatment of childhood central nervous system atypical teratoid and rhabdoid tumor. It is intended as a resource to inform and assist clinicians in the care of their patients. It does not provide formal guidelines or recommendations for making health care decisions.
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PDQ® Pediatric Treatment Editorial Board. PDQ Childhood Central Nervous System Atypical Teratoid/Rhabdoid Tumor Treatment. Bethesda, MD: National Cancer Institute. Updated <MM/DD/YYYY>. Available at: https://www.cancer.gov/types/brain/hp/child-cns-atrt-treatment-pdq. Accessed <MM/DD/YYYY>. [PMID: 26389426]
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