Mutations of the hSNF5/INI1 gene in renal rhabdoid tumors with second primary brain tumors

Novel Strategy Involving High-Dose Chemotherapy with Stem Cell Rescue Followed by Intrathecal Topotecan Maintenance Therapy without Whole-Brain Irradiation for Atypical Teratoid/Rhabdoid Tumors

Atypical teratoid/rhabdoid tumor (AT/RT) is a rare aggressive central nervous system tumor that typically affects children under three years old and has poor survival with a high risk for neurologic deficits. The primary purpose of this study was to successfully treat the disease and delay or avoid whole-brain radiotherapy for children with AT/RT. A retrospective analysis was performed for six children diagnosed with AT/RT and treated with multimodal treatment at a single institute between 2014 and 2020. Furthermore, germline SMARCB1 aberrations and MGMT methylation status of the tumors were analyzed. One patient who did not receive a modified IRS-III regimen replaced with ifosphamide, carboplatin, and etoposide (ICE) in induction chemotherapy was excluded from this analysis. Five patients who received ICE therapy were under three years old. After a surgical approach, they received intensive chemotherapy and high-dose chemotherapy with autologous peripheral blood stem cell transplantation (HDCT/autoPBSCT) followed by intrathecal topotecan maintenance therapy. Three patients underwent single HDCT/autoPBSCT, and the other two received sequential treatment. Two patients with germline SMARCB1 aberrations and metastases died of progressive AT/RT or therapy-related malignancy, while 3 with localized tumors without germline SMARCB1 aberrations remained alive. One survivor received local radiotherapy only, while the other two did not undergo radiotherapy. All three surviving patients were able to avoid whole-brain radiotherapy. Our results suggest that AT/RT patients with localized tumors without germline SMARCB1 aberrations can be rescued with multimodal therapy, including induction therapy containing ICE followed by HDCT/autoPBSCT and intrathecal topotecan maintenance therapy without radiotherapy. Further large-scale studies are necessary to confirm this hypothesis.

Case Analysis of 14 Children with Malignant Rhabdoid Tumor of the Kidney

Objective

This study aims to summarize the clinical features and prognoses of the malignant rhabdoid tumor of the kidney (MRTK) in children. It further aims to analyze the high-risk factors affecting MRTK prognosis.

Methods

Clinical data from 14 children with MRTK treated in Paediatrics of Beijing Tongren Hospital from January 2010 to December 2019, along with the high-risk factors affecting prognosis, were retrospectively analyzed.

Results

There were 14 children with MRTK included in the study, with a median onset age of 13 (3–46) months. Thirteen patients had distant metastases, the most common site for metastases being inside the lung. A comprehensive treatment protocol combined with chemotherapy was mainly applied during the surgery. A surgical resection of primary tumors was performed on 13 (13/14) patients, and all 14 children received chemotherapy with ifosfamide + carboplatin + etoposide, ifosfamide + etoposide, and vincristine + pirarubicin + cyclophosphamide regimens, alternately. Three patients received radiotherapy and two received oral targeted drugs after partial response. The median follow-up was after 16.5 months (3–53 months) and the four-year overall survival (OS) was 41.8%. In children aged ≤24 months and children aged >24 months, the two-year OS was 67.2% and 100% (χ² = 108.998, P<0.05), respectively. In children with Ki 67 > 70% and children with Ki 67 < 70%, the two-year OS was 52.6% and 86.9% (χ² = 8.544, P = 0.003), respectively. In children with distant metastases and children without distant metastasis, the two-year OS was 70% and 100% (χ² = 14.239, P<0.05), respectively.

Conclusion

The most common MRTK distant metastasis site is the lung. Risk factors for poor MRTK prognoses include an age of <24 months, Ki 67 > 70%, and distant metastases.

Germline Genetics and Childhood Cancer: Emerging Cancer Predisposition Syndromes and Psychosocial Impacts

PURPOSE OF REVIEW

Germline genetic variants contribute to a substantial proportion of cases of cancer in childhood. The purpose of this review is to describe two emerging pediatric cancer predisposition syndromes, including published surveillance protocols, as well as the psychological impacts related to childhood cancer predisposition.

RECENT FINDINGS

DICER1 syndrome is pleotropic, predisposing to a variety of tumors and likely phenotypically broader than currently realized. Rhabdoid tumor predisposition syndrome carries a risk for development of aggressive malignancies occurring in nearly any tissue. New pediatric hereditary cancer syndromes are likely to be identified as genetic evaluation evolves. Advantages and disadvantages of genetic testing and surveillance protocols need to be discussed with patients and families in a team-based approach, with the input of a genetic counselor holding expertise in pediatric cancer predisposition. Finally, literature on psychosocial impacts of hereditary cancer syndromes in pediatric patients is sparse, necessitating further research.

SWI/SNF Complex-Deficient Soft Tissue Neoplasms: A Pattern-Based Approach to Diagnosis and Differential Diagnosis

Loss of different components of the Switch/sucrose nonfermentable (SWI/SNF) chromatin remodeling complex has been increasingly recognized as a central molecular event driving the initiation and/or dedifferentiation of mostly lethal but histogenetically diverse neoplasms in different body organs. This review summarizes and discusses the morphologic and phenotypic diversity of primary soft tissue neoplasms characterized by SWI/SNF complex deficiency with an emphasis on convergent and divergent cytoarchitectural patterns.

Malignant rhabdoid tumors originating within and outside the central nervous system are clinically and molecularly heterogeneous

Multifocal synchronous or metachronous atypical teratoid rhabdoid tumors (ATRTs) and non-central nervous system malignant rhabdoid tumors (extra-CNS MRTs) are rare cancers. We reviewed the clinical and radiologic characteristics of affected patients seen at our institution. Genotyping and analysis of copy number abnormalities (CNAs) in SMARCB1 were performed in germline and tumor samples. Tumor samples underwent genome-wide DNA methylation and CNA analysis. The median age at diagnosis of 21 patients was 0.6 years. Two-thirds of ATRTs and extra-CNS MRTs were diagnosed synchronously. Although kidney tumors predominated, including two patients with bilateral involvement, at least 30% of cases lacked renal involvement. Histopathologic review confirmed MRTs in all cases and INI1 expression loss in all tumors tested. Fourteen (78%) of 18 patients tested had heterozygous germline SMARCB1 abnormalities. At least one allelic SMARCB1 abnormality was confirmed in 81 and 88% of ATRTs and extra-CNS MRTs, respectively. Unsupervised hierarchical clustering analysis of DNA methylation in 27 tumors and comparison with a reference group of 150 ATRTs classified the CNS tumors (n = 14) as sonic hedgehog (64%), tyrosinase (21%), and MYC (14%). The MYC subgroup accounted for 85% of 13 extra-CNS MRTs. Of 16 paired ATRTs and extra-CNS MRTs, the tumors in seven of eight patients showed a different pattern of genome-wide DNA methylation and/or CNAs suggestive of non-clonal origin. CNS and extra-CNS tumors had an identical SMARCB1 amplification (n = 1) or very similar DNA methylation pattern (n = 1) suggestive of clonal origin. All patients died of tumor progression. The clinical and molecular characteristics of multifocal ATRTs and extra-CNS MRTs are heterogeneous with most patients harboring a cancer predisposition. Although independent tumor origin was confirmed in most cases, metastatic spread was also documented. The recognition of their distinct molecular characteristics is critical in selecting new biologic therapies against these deadly cancers.

A Comprehensive Review of Pediatric Tumors and Associated Cancer Predisposition Syndromes

An understanding of the role of inherited cancer predisposition syndromes in pediatric tumor diagnoses continues to develop as more information is learned through the application of genomic technology. Identifying patients and their relatives at an increased risk for developing cancer is an important step in the care of this patient population. The purpose of this review is to highlight various tumor types that arise in the pediatric population and the cancer predisposition syndromes associated with those tumors. The review serves as a guide for recognizing genes and conditions to consider when a pediatric cancer referral presents to the genetics clinic.

The molecular pathogenesis of schwannomatosis, a paradigm for the co-involvement of multiple tumour suppressor genes in tumorigenesis

Schwannomatosis is characterized by the predisposition to develop multiple schwannomas and, less commonly, meningiomas. Despite the clinical overlap with neurofibromatosis type 2 (NF2), schwannomatosis is not caused by germline NF2 gene mutations. Instead, germline mutations of either the SMARCB1 or LZTR1 tumour suppressor genes have been identified in 86% of familial and 40% of sporadic schwannomatosis patients. In contrast to patients with rhabdoid tumours, which are due to complete loss-of-function SMARCB1 mutations, individuals with schwannomatosis harbour predominantly hypomorphic SMARCB1 mutations which give rise to the synthesis of mutant proteins with residual function that do not cause rhabdoid tumours. Although biallelic mutations of SMARCB1 or LZTR1 have been detected in the tumours of patients with schwannomatosis, the classical two-hit model of tumorigenesis is insufficient to account for schwannoma growth, since NF2 is also frequently inactivated in these tumours. Consequently, tumorigenesis in schwannomatosis must involve the mutation of at least two different tumour suppressor genes, an occurrence frequently mediated by loss of heterozygosity of large parts of chromosome 22q harbouring not only SMARCB1 and LZTR1 but also NF2. Thus, schwannomatosis is paradigmatic for a tumour predisposition syndrome caused by the concomitant mutational inactivation of two or more tumour suppressor genes. This review provides an overview of current models of tumorigenesis and mutational patterns underlying schwannomatosis that will ultimately help to explain the complex clinical presentation of this rare disease.

Rhabdoid tumor predisposition syndrome

Rhabdoid tumors (RT), or malignant rhabdoid tumors, are among the most aggressive and lethal forms of human cancer. They can arise in any location in the body but are most commonly observed in the brain, where they are called atypical teratoid/rhabdoid tumors (AT/RT), and in the kidneys, where they are called rhabdoid tumors of the kidney. The vast majority of rhabdoid tumors present with a loss of function in the SMARCB1 gene, also known as INI1, BAF47, and hSNF5, a core member of the SWI/SNF chromatin-remodeling complex. Recently, mutations in a 2nd locus of the SWI/SNF complex, the SMARCA4 gene, also known as BRG1, were found in rhabdoid tumors with retention of SMARCB1 expression. Familial cases may occur in a condition known as rhabdoid tumor predisposition syndrome (RTPS). In RTPS, germline inactivation of 1 allele of a gene occurs. When the mutation occurs in the SMARCB1 gene, the syndrome is called RTPS1, and when the mutation occurs in the SMARCA4 gene it is called RTPS2. Children presenting with RTPS tend to develop tumors at a younger age, but the impact that germline mutation has on survival remains unclear. Adults who carry the mutation tend to develop multiple schwannomas. The diagnosis of RTPS should be considered in patients with RT, especially if they have multiple primary tumors, and/or in individuals with a family history of RT. Because germline mutations result in an increased risk of carriers developing RT, genetic counseling for families with this condition is recommended.

The expanding family of SMARCB1(INI1)-deficient neoplasia: implications of phenotypic, biological, and molecular heterogeneity

Since the description of atypical teratoid/rhabdoid tumors of the central nervous system and renal/extrarenal malignant rhabdoid tumors in children, the clinicopathologic spectrum of neoplasms having in common a highly variable rhabdoid cell component (0% to 100%) and consistent loss of nuclear SMARCB1 (INI1) expression has been steadily expanding to include cribriform neuroepithelial tumor of the ventricle, renal medullary carcinoma and a subset of collecting duct carcinoma, epithelioid sarcoma, subsets of miscellaneous benign and malignant soft tissue tumors, and rare rhabdoid carcinoma variants of gastroenteropancreatic, sinonasal, and genitourinary tract origin. Although a majority of SMARCB1-deficient neoplasms arise de novo, the origin of SMARCB1-deficient neoplasia in the background of a phenotypically or genetically definable differentiated SMARCB1-intact "parent neoplasm" has been convincingly demonstrated, highlighting the rare occurrence of rhabdoid tumors as "double-hit neoplasia." As a group, SMARCB1-deficient neoplasms occur over a wide age range (0 to 80 y), may be devoid of rhabdoid cells or display uniform rhabdoid morphology, and follow a clinical course that varies from benign to highly aggressive causing death within a few months irrespective of aggressive multimodality therapy. Generally applicable criteria that would permit easy recognition of these uncommon neoplasms do not exist. Diagnosis is based on site-specific and entity-specific sets of clinicopathologic, immunophenotypic, and/or molecular criteria. SMARCB1 immunohistochemistry has emerged as a valuable tool in confirming or screening for SMARCB1-deficient neoplasms. This review summarizes the different phenotypic and topographic subgroups of SMARCB1-deficient neoplasms including sporadic and familial, benign and malignant, and rhabdoid and nonrhabdoid variants, highlighting their phenotypic heterogeneity and molecular complexity.

Establishment and characterization of MRT cell lines from genetically engineered mouse models and the influence of genetic background on their development

Malignant rhabdoid tumors (MRTs) are rare, aggressive cancers occuring in young children primarily through inactivation of the SNF5(INI1, SMARCB1) tumor suppressor gene. We and others have demonstrated that mice heterozygous for a Snf5 null allele develop MRTs with partial penetrance. We have also shown that Snf5(+/-) mice that lack expression of the pRb family, due to TgT121 transgene expression, develop MRTs with increased penetrance and decreased latency. Here, we report that altering the genetic background has substantial effects upon MRT development in Snf5(+/--) and TgT121 ;Snf5(+/-) mice, with a mixed F1 background resulting in increased latency and the appearance of brain tumors. We also report the establishment of the first mouse MRT cell lines that recapitulate many features of their human counterparts. Our studies provide further insight into the genetic influences on MRT development as well as provide valuable new cell culture and genetically engineered mouse models for the study of CNS-MRT etiology.

Rhabdoid tumors of the liver: rare, aggressive, and poorly responsive to standard cytotoxic chemotherapy

BACKGROUND

Rhabdoid tumors of the liver are rare tumors that are difficult to cure. We compiled all the cases previously reported in the literature to review clinical data, treatments, and outcomes.

PROCEDURE

Patients were identified by literature review using PubMed.

RESULTS

Thirty-four patients were identified. The median age at presentation was 8 months. All patients with reported AFP results exhibited normal or minimally increased serum AFP levels. All 10 tumors with reported INI1 immunohistochemistry results were reported as negative. Twenty-one patients presented with metastatic disease at diagnosis. Thirty patients died of disease or treatment complications. Most deaths occurred within 12 months after diagnosis. Five patients survived at the time of the reports with one patient alive with disease. One patient relapsed and subsequently died after the report was published. Of the four patients alive without disease, all were treated with chemotherapy, and at least three had surgery or transplantation. Two patients received radiation therapy but did not survive.

CONCLUSIONS

Rhabdoid tumors of the liver are aggressive, rare tumors of the infant liver that are often associated with metastases at the time of diagnosis. Mortality is high and often occurs soon after diagnosis. Treatment with aggressive chemotherapy in combination (especially an alkylating agents doxorubicin) with complete resection may lead to improved outcomes. Therapy targeted to the INI1 mutation of these tumors is currently being investigated and may offer greater hope of cure.

Congenital anomalies and rhabdoid tumor associated with 22q11 germline deletion and somatic inactivation of the SMARCB1 tumor suppressor

The most common microdeletion in humans involves the 22q11 region. Congenital anomalies associated with 22q11 loss include cardiac and facial defects. Less frequent is the co-presentation of malignant rhabdoid tumors that are highly aggressive childhood malignancies typically found in renal or extra-renal soft tissues and central nervous system. A newborn patient presented with multiple congenital anomalies consistent with 22q11 deletion syndrome including cleft lip and palate, ear tags and ventricular septal defects co-presenting with an axillary rhabdoid tumor. Comparative genomic hybridization revealed a 2.8 Mb germline deletion in the 22q11.2 region containing genes required for normal fetal development and the SMARCB1 tumor suppressor gene. Analysis of tumor DNA revealed a somatic deletion of exon 7 in the second allele of SMARCB1. Expression of SMARCB1 was absent, while tumor markers including MYC, GFAP, and CLAUDIN-6 were upregulated. The presence of tandem oriented BCRL modules located within interspersed low copy repeat elements throughout the 22q11 distal region may predispose this area for microdeletions through nonalleleic homologous recombination.

Germline nonsense mutation and somatic inactivation of SMARCA4/BRG1 in a family with rhabdoid tumor predisposition syndrome

Rhabdoid tumors of early infancy are highly aggressive with consequent poor prognosis. Most cases show inactivation of the SMARCB1 (also known as INI1 and hSNF5) tumor suppressor, a core member of the ATP-dependent SWI/SNF chromatin-remodeling complex. Familial cases, described as rhabdoid tumor predisposition syndrome (RTPS), have been linked to heterozygous SMARCB1 germline mutations. We identified inactivation of another member of the SWI/SNF chromatin-remodeling complex, its ATPase subunit SMARCA4 (also known as BRG1), due to a SMARCA4/BRG1 germline mutation and loss of heterozygosity by uniparental disomy in the tumor cells of two sisters with rhabdoid tumors lacking SMARCB1 mutations. SMARCA4 is thus a second member of the SWI/SNF complex involved in cancer predisposition. Its general involvement in other tumor entities remains to be established.

Hijacking the chromatin remodeling machinery: impact of SWI/SNF perturbations in cancer

There is increasing evidence that alterations in chromatin remodeling play a significant role in human disease. The SWI/SNF chromatin remodeling complex family mobilizes nucleosomes and functions as a master regulator of gene expression and chromatin dynamics whose functional specificity is driven by combinatorial assembly of a central ATPase and association with 10 to 12 unique subunits. Although the biochemical consequence of SWI/SNF in model systems has been extensively reviewed, the present article focuses on the evidence linking SWI/SNF perturbations to cancer initiation and tumor progression in human disease.

Schwannomatosis associated with multiple meningiomas due to a familial SMARCB1 mutation

Schwannomatosis (MIM 162091) is a condition predisposing to the development of central and peripheral schwannomas; most cases are sporadic without a clear family history but a few families with a clear autosomal dominant pattern of transmission have been described. Germline mutations in SMARCB1 are associated with schwannomatosis. We report a family with multiple schwannomas and meningiomas. A SMARCB1 germline mutation in exon 1 was identified. The mutation, c.92A>T (p.Glu31Val), occurs in a highly conserved amino acid in the SMARCB1 protein. In addition, in silico analysis demonstrated that the mutation disrupts the donor consensus sequence of exon 1. RNA studies verified the absence of mRNA transcribed by the mutant allele. This is the first report of a SMARCB1 germline mutation in a family with schwannomatosis characterized by the development of multiple meningiomas.

The role of INI1/hSNF5 in gene regulation and cancer

The precise modulation of chromatin dynamics is an essential and complex process that ensures the integrity of transcriptional regulation and prevents the transition of a normal cell into a cancerous one. ATP-dependent chromatin remodeling enzymes are multisubunit complexes that play a pivotal role in this operation through the mobilization of nucleosomes to promote DNA accessibility. Chromatin remodeling is mediated by the interaction of DNA-binding factors and individual members of this complex, directing its targeted recruitment to specific regulatory regions. In this review, we discuss a core subunit of the SWI/SNF ATP-dependent chromatin remodeling complex, known as INI1/hSNF5, in the context of transcriptional regulation and impact on cancer biology. In particular, we review current knowledge of the diverse protein interactions between INI1/hSNF5 and viral and cellular factors, with a special emphasis on the potent oncogene c-Myc.

Imprinted CDKN1C is a tumor suppressor in rhabdoid tumor and activated by restoration of SMARCB1 and histone deacetylase inhibitors

SMARCB1 is deleted in rhabdoid tumor, an aggressive paediatric malignancy affecting the kidney and CNS. We hypothesized that the oncogenic pathway in rhabdoid tumors involved epigenetic silencing of key cell cycle regulators as a consequence of altered chromatin-remodelling, attributable to loss of SMARCB1, and that this hypothesis if proven could provide a biological rationale for testing epigenetic therapies in this disease. We used an inducible expression system to show that the imprinted cell cycle inhibitor CDKN1C is a downstream target for SMARCB1 and is transcriptionally activated by increased histone H3 and H4 acetylation at the promoter. We also show that CDKN1C expression induces cell cycle arrest, CDKN1C knockdown with siRNA is associated with increased proliferation, and is able to compete against the anti-proliferative effect of restored SMARCB1 expression. The histone deacetylase inhibitor (HDACi), Romidepsin, specifically restored CDKN1C expression in rhabdoid tumor cells through promoter histone H3 and H4 acetylation, recapitulating the effect of SMARCB1 on CDKNIC allelic expression, and induced cell cycle arrest in G401 and STM91-01 rhabdoid tumor cell lines. CDKN1C expression was also shown to be generally absent in clinical specimens of rhabdoid tumor, however CDKN1A and CDKN1B expression persisted. Our observations suggest that maintenance of CDKN1C expression plays a critical role in preventing rhabdoid tumor growth. Significantly, we report for the first time, parallels between the molecular pathways of SMARCB1 restoration and Romidepsin treatment, and demonstrate a biological basis for the further exploration of histone deacetylase inhibitors as relevant therapeutic reagents in the treatment of rhabdoid tumor.

Alterations in the SMARCB1 (INI1) tumor suppressor gene in familial schwannomatosis

Schwannomatosis is a third major form of neurofibromatosis that has recently been linked to mutations in the SMARCB1 (hSnf5/INI1) tumor suppressor gene. We analyzed the coding region of SMARCB1 by direct sequencing and multiplex ligation-dependent probe amplification (MLPA) in genomic DNA from 19 schwannomatosis kindreds. Microsatellite markers in the SMARCB1 region were developed to determine loss of heterozygosity (LOH) in associated tumors. We detected four alterations in conserved splice acceptor or donor sequences of exons 3, 4 and 6. Two alterations that likely affect splicing were seen in introns 4 and 5. An additional four alterations of unclear pathogenicity were found to segregate on the affected allele in eight families including two non-conservative missense alterations in three families. No constitutional deletions or duplications were detected by MLPA. Nine of 13 tumors examined showed partial LOH of the SMARCB1 region consistent with 'second hits.' Alterations were detected in tumors both with and without somatic NF2 gene changes. These findings support the hypothesis that SMARCB1 is a tumor suppressor for schwannomas in the context of familial disease. Further work is needed to determine its role in other multiple and single tumor syndromes.

Renal tumours of childhood: an update

The role of the pathologist has been fundamental in the progress of the treatment of paediatric renal tumours. There are different philosophies in the treatment of these tumours, and there have been many recent advances in the areas of chemotherapy, identification of new entities, prognostic histological criteria following treatment and molecular prognostic and diagnostic features. This review discusses the different approaches of the different treatment protocols from Europe and North America, and reviews staging criteria, prognostic criteria and also the different tumour entities.

Evidence of a four-hit mechanism involving SMARCB1 and NF2 in schwannomatosis-associated schwannomas

Schwannomatosis is characterized by the onset of multiple intracranial, spinal, or peripheral schwannomas, without involvement of the vestibular nerve, which is instead pathognomonic of neurofibromatosis type 2 (NF2). Recently, a schwannomatosis family with a germline mutation of the SMARCB1 gene on chromosome 22 has been described. We report on the molecular analysis of the SMARCB1 and NF2 genes in a series of 21 patients with schwannomatosis and in eight schwannomatosis-associated tumors from four different patients. A novel germline SMARCB1 mutation was found in one patient; inactivating somatic mutations of NF2, associated with loss of heterozygosity (LOH) of 22q, were found in two schwannomas of this patient. This is the second report of a germline SMARCB1 mutation in patients affected by schwannomatosis and the first report of SMARCB1 mutations associated with somatic NF2 mutations in schwannomatosis-associated tumors. The latter observation suggests that a four-hit mechanism involving the SMARCB1 and NF2 genes may be implicated in schwannomatosis-related tumorigenesis.

Long-term survival and transmission of INI1-mutation via nonpenetrant males in a family with rhabdoid tumour predisposition syndrome

Rhabdoid tumour predisposition syndrome (RTPS) is a rare syndrome caused by inheritance of a mutated INI1 gene for which only two multigeneration families have been reported. To further characterise the genotype and phenotype of RTPS, we present a third family in which at least three cousins developed an atypical teratoid/rhabdoid tumour (AT/RT) at a young age. Two of these patients showed unusual long survival, and one of these developed an intracranial meningioma and a myoepithelioma of the lip in adulthood. Mutation analysis of INI1 revealed a germline G>A mutation in the donor splice site of exon 4 (c.500+1G>A) in the patients and in their unaffected fathers. This mutation prevents normal splicing and concomitantly generates a stop codon, resulting in nonsense-mediated mRNA decay. Biallelic inactivation of INI1 in the tumours, except for the meningioma, was confirmed by absence of nuclear INI1-protein staining. The myoepithelioma of one of the patients carried an identical somatic rearrangement in the NF2 gene as the AT/RT, indicating that both tumours originated from a common precursor cell. In conclusion, this study demonstrates for the first time transmission of a germline INI1-mutation in a RTPS family via nonpenetrant males, long-term survival of two members of this family with an AT/RT, and involvement of INI1 in the pathogenesis of myoepithelioma.

Part I: Primary malignant non-Wilms' renal tumours in children

Non-Wilms' tumours form a small heterogeneous group of clinically significant renal malignancies in children, including renal-cell carcinoma, clear-cell sarcoma, (congenital) mesoblastic nephroma, rhabdoid tumour, and renal medullary carcinoma. Good progress has been made in the assessment of these tumours, which has led to a greater understanding of the molecular changes that occur in their development. This review is the first of two parts, and provides an updated review of the clinical presentation, imaging, and pathology of these tumours.

Tumor-specific cooperation of retinoblastoma protein family and Snf5 inactivation

Malignant rhabdoid tumors (MRT) are rare aggressive cancers that occur in young children. Seventy-five percent of sporadic MRTs harbor inactivating SNF5 mutations, and mice heterozygous for an Snf5-null allele develop MRTs with partial penetrance. The diagnosis of choroid plexus carcinomas (CPC) in addition to MRTs in families with a single mutant SNF5 allele prompted us to assess the role of SNF5 loss in CPC in genetically engineered mice. With high frequency, TgT(121) mice develop CPCs that are initiated by inactivation of retinoblastoma protein (pRb) and related proteins p107 and p130. However, CPC penetrance and latency were not significantly affected by Snf5 heterozygosity, consistent with recent evidence that CPCs in SNF5 families were, in many cases, misdiagnosed MRTs. Surprisingly, although the CPC phenotype was unaffected, TgT(121);Snf5(+/-) mice developed MRTs with increased penetrance and decreased latency compared with TgT(121);Snf5(+/+) littermates. MRTs expressed the T(121) protein with a concomitant increase in mitotic activity. The predominant appearance of TgT(121);Snf5(+/-) MRTs in the spinal cord led to the discovery that these tumors likely arose from a subset of spinal cord neural progenitor cells expressing T(121) rather than from transdifferentiation of CPC. Significantly, the target cell type(s) for MRT is unknown. Hence, this study not only shows that pRb(f) and SNF5 inactivation cooperate to induce MRTs but also provides new insight into the MRT target population.

Predisposition to atypical teratoid/rhabdoid tumor due to an inherited INI1 mutation

BACKGROUND

Germline mutations of the INI1 gene predispose children to the development of rhabdoid tumors. Reports of familial cases, however, are extremely rare.

PROCEDURE

We have identified a three-generation family in which two half-brothers were diagnosed with central nervous system atypical teratoid/rhabdoid tumors (AT/RT). The two boys, diagnosed at 2 months and 17 months of age, had a germline insertion mutation in exon 4 of the INI1 gene that was inherited from their healthy mother. A maternal uncle died in childhood from a brain tumor and a malignant rhabdoid tumor of the kidney, and presumably carried the same germline mutation. As the mother and uncle had different fathers, the grandmother is also an obligate carrier of the mutation.

CONCLUSION

The identification of two unaffected carriers in a family segregating a germline mutation and rhabdoid tumor supports the hypothesis that there may be variable risks of development of rhabdoid tumor in the context of a germline mutation. There may be a developmental window in which most rhabdoid tumors occur. This family highlights the importance of mutation analysis in all patients with a suspected rhabdoid tumor.

Non-linkage of familial rhabdoid tumors to SMARCB1 implies a second locus for the rhabdoid tumor predisposition syndrome

BACKGROUND

Rhabdoid tumors represent an independent entity among embryonal neoplasms. These tumors affect the kidney (RTK, rhabdoid tumor of kidney) and central nervous system (AT/RT, atypical teratoid, rhabdoid tumor), but may also be found in peripheral soft tissue. Unifying features include immunohistochemical characteristics and inactivation of the putative tumor suppressor gene SMARCB1 (hSNF5/INI1) in chromosome 22q11.2. Several familial cases have been published and summarized under the term rhabdoid tumor predisposition syndrome. In all of the published familial cases, inactivation of SMARCB1 was detected in tumor tissues.

PROCEDURE AND RESULTS

We report on a family with three children, two of which were affected by rhabdoid tumors, one RTK, the other an AT/RT. While both children demonstrated typical morphological and clinical features neither the RTK nor the AT/RT showed evidence for inactivation of SMARCB1 in molecular studies including CGH and array CGH, FISH, gene dosage analysis by dHPLC, and DNA-sequencing. Immunohistochemistry for SMARCB1 showed normal expression within the nuclei of tumor cells. Furthermore, both children inherited different paternal and maternal SMARCB1 alleles evidenced by haplotype analysis. Conventional cytogenetic, FISH, and mutation analyses lacked evidence for SMARCB1 aberrations or gross chromosomal changes in the parents.

CONCLUSIONS

We thus demonstrate a family with rhabdoid tumor predisposition syndrome without linkage to SMARCB1. This finding indicates that other loci than SMARCB1 below the resolution of array CGH are involved in the origin of these tumors. Our data impact on the clinical counseling of affected families and warrant further studies in the molecular biology of these enigmatic tumors.

Atypical teratoid/rhabdoid tumors and choroid plexus tumors: when genetics "surprise" pathology

Atypical teratoid/rhabdoid tumor (ATRT) and choroid plexus tumors (CPT) represent, so far, 2 well defined types of CNS neoplasm on the basis of their histological features and clinical presentation (10). While CPTs are intraventricular epithelial tumors arising from choroid plexus epithelium, the cellular origin of ATRTs is still unknown. Inactivating mutations of the hSNF5/INI-1 gene located in the chromosomal region 22q11.2 are regarded as a crucial step in the molecular pathogenesis of ATRTs; the genetic changes associated with CPTs are largely unknown. However, the recent finding of inactivation of hSNF5/INI-1 in choroid plexus carcinomas and papillomas (9, 18) points to a closer relationship between these 2 entities. This is supported by the occurence of choroid plexus carcinomas (CPC) in the setting of families with rhabdoid predisposition syndrome (RPS), (19) caused by germ line inactivation of the INI1 gene.

Atypical teratoid rhabdoid tumors of childhood: diagnosis, treatment and challenges

Atypical teratoid rhabdoid tumor of the brain was described as a unique entity in the late 1980s. It occurs primarily in early childhood but the true incidence of the disease is not yet known. At presentation, the differential diagnosis includes medulloblastoma, primitive neuroectodermal tumor, ependymoma and choroid plexus carcinoma. Atypical teratoid rhabdoid tumor behaves in a very aggressive manner and while cure is possible for a small minority of patients, no standard or effective therapy has been defined for most patients. Since its first description, considerable pathologic, cytogenetic and molecular characterizations, as described in this review, have been accomplished that provide insight into the possible molecular etiology of the disease and of malignant rhabdoid tumors that occur outside the CNS. Co-operative group clinical trials that focus solely on atypical teratoid rhabdoid tumor are needed that incorporate biologic studies along with evaluations of aggressive treatment approaches. The goal of these trials should be to increase the cure rate for children with atypical teratoid rhabdoid tumor and further increase our understanding not only of atypical teratoid rhabdoid tumor, but also of other pediatric brain tumors.

Molecular genetics of atypical teratoid/rhabdoid tumors

Rhabdoid tumors are extremely aggressive malignancies that generally occur in infants and young children. The most common locations are the kidney and central nervous system (atypical teratoid/rhabdoid tumor [RT]), although RTs can also arise in most soft-tissue sites. Rhabdoid tumors in all anatomical locations have a similar molecular origin. Mutation or deletion of both copies of the hSNF5/INI1 gene that maps to chromosome band 22q11.2 is observed in approximately 70% of primary tumors. An additional 20 to 25% of tumors have reduced expression at the RNA or protein level, indicative of a loss-of-function event. The INI1 protein is a component of the SWI/SNF chromatin-remodeling complex. The complex is recruited to promoters of a large variety of genes involved in cell signaling, growth, and differentiation. This review summarizes what is currently known regarding the molecular genetics of RTs.

Rhabdoid tumor of the kidney in the National Wilms' Tumor Study: age at diagnosis as a prognostic factor

PURPOSE

The objective of this study is to determine prognostic factors in rhabdoid tumor of the kidney (RTK), including both demographic and treatment variables.

PATIENTS AND METHODS

A total of 142 patients studied on National Wilms' Tumor Studies 1, 2, 3, 4, and 5 were analyzed. Patients were enrolled between the years 1969 and 2002. Variables examined included sex, age of diagnosis, tumor stage, presence of CNS lesions, as well as treatment variables, including the use of doxorubicin and/or radiotherapy (RT).

RESULTS

No survival differences were observed between males and females, between those treated with or without doxorubicin, or with or without RT. Patients with tumors of lower stage had an overall survival rate of 41.8%, whereas, tumors of higher stage were associated with a 15.9% survival (P < .001). A highly significant difference in survival was noted when patients were stratified according to age of diagnosis. Survival at 4 years in infants under 6 months of age at diagnosis was 8.8%, whereas, survival in patients 2 years of age or older was 41.1% (P < .0001). Stratification into intermediate age brackets demonstrated a strong correlation of increasing survival with increasing age at diagnosis. All patients with a CNS lesion, except one, died.

CONCLUSION

Age at diagnosis is a highly significant prognostic factor for survival of children with RTK. Infants have a dismal prognosis, whereas, older children have a more favorable outcome. Higher tumor stage and presence of a CNS lesion were both factors predictive of a poor survival rate.

Cyclin D1 is overexpressed in atypical teratoid/rhabdoid tumor with hSNF5/INI1 gene inactivation

OBJECT

Although atypical teratoid/rhabdoid tumor (AT/RT) is known to generate through inactivation of the hSNF5/INI1 gene on chromosome 22q, the downstream molecular mechanism remains unclear. We histologically and molecularly reviewed our pediatric brain tumors for unrecognized AT/RTs and evaluated the role of cyclin D1, a potential molecular target of hSNF5/INI1.

METHODS

We analyzed 16 tumors under three years of age: seven medulloblastomas, three anaplastic ependymomas (E IIIs), two each of supratentorial primitive neuroectodermal tumors (sPNETs) and choroid plexus carcinomas (CPCs), and one each of neuroblastoma and pineoblastoma. Immunohistochemistry for glial fibrillary acidic protein, vimentin, epithelial membrane antigen, smooth muscle actin and cyclin D1 was performed. Polymerase chain reaction (PCR)-single-strand conformation polymorphism analysis with direct sequencing, differential PCR and microsatellite analysis were conducted for hSNF5/INI1mutation, homozygous deletion and loss of heterozygosity (LOH) on 22q, respectively. Because of the presence of rhabdoid cells and the polyimmunophenotypic features, the diagnosis was revised to AT/RT in five (31%) tumors, namely, two E IIIs and one each of medulloblastoma, CPC and pineoblastoma. Three of them harbored such hSNF5/INI1 aberrations as germline single base deletion (492/6 delC) and missense mutation (C157T) together with LOH 22q or homozygous deletion. Cyclin D1 was overexpressed in those three tumors but not in the two that lacked hSNF5/INI1 inactivation.

CONCLUSION

AT/RT can be misdiagnosed as a variety of tumors, including ependymoma that potentially harbors LOH 22q. Our data indicate that cyclin D1 is a target of hSNF5/INI1in primary tumors.

[Kidney tumors in childhood]

Types of renal tumors arising in children are different from those occurring in adults. Nephroblastoma is the most common (85%) with a clinical outcome which has dramatically improved in the last 30 years. Current classifications are aimed at better adaptation of treatment to each individual case, reducing iatrogenic complications without impairing total cure. Amongst entities which have been recently described or are better known we can find juvenile carcinoma associated with Xp11.2 translocation, renal medullary carcinoma, metanephric tumors, etc. Role of molecular cytogenetics is increasing for classification (and treatment) and this should always be kept in mind when dealing a fresh specimen of childhood renal tumor.

Chromosome mechanisms and INI1 inactivation in human and mouse rhabdoid tumors

The human rhabdoid tumorigenesis orchestrated by INI1 inactivation is associated with specific rearrangements of chromosome 22 that correlate with preferential anatomic tumor locations. A literature review revealed significant correlations between an apparently normal karyotype and kidney tumors, monosomy 22 and cerebral tumors, and chromosome 22 translocations and tumors at other anatomic sites. In the mouse rhabdoid tumor model, specifically in the four tumors that we tested for loss of heterozygosity, neither partial deletion nor monosomy of chromosome 10 could be detected. In contrast to the human data, the only chromosome mechanism involved in the 18 mouse tumors studied appears to be a mitotic recombination or a nondisjunction-duplication. Additionally, and despite mouse tumor incidence across a variety of sites, no rhabdoid tumor could be observed in the mouse kidney. These data suggest that the chromosome mechanisms for INI1 inactivation and the selective cell survival pressure differ in human and mouse.

Pediatric embryonal tumor with epithelial immunophenotype showing absence of hSNF5/INI1 expression

CASE REPORT

A case of a histologically unclassified brain tumor in a 32-month-old boy is reported. He presented with vomiting, appetite loss, and right motor weakness. MR images revealed a huge mass in the left frontoparietal region that was enhanced after the administration of Gd-DTPA. The mass was removed three times because of its recurrence.

RESULTS

Histologically, the tumor was composed largely of small-undifferentiated round cells without any patterns of differentiation. Immunohistochemically, the tumor cells were positive for cytokeratin and focally for epithelial membrane antigen (EMA). Glial fibrillary acidic protein (GFAP), S-100 protein and neuronal markers were negative. Electron microscopic investigations demonstrated no evidence of specific differentiation. MIB-1 staining index was 10-40%. The origin of the tumor was not detected. Expression of the hSNF5/INI1 of this tumor was not detected by reverse transcription-polymerase chain reaction (RT-PCR). The patient has been in a good condition for 7 years after the first operation.

CONCLUSIONS

Based on the immunohistochemical findings, the tumor was descriptively diagnosed as an embryonal tumor with an epithelial immunophenotype. The hSNF5/INI1 gene has recently been reported to act as a tumor suppressor in atypical teratoid/rhabdoid tumors. The hSNF5/INI1 gene may lead to tumorigenesis in this case.

Novel germ-line deletion ofSNF5/INI1/SMARCB1 gene in neonate presenting with congenital malignant rhabdoid tumor of kidney and brain primitive neuroectodermal tumor

We describe a neonate who had a rare tumor combination of a malignant rhabdoid tumor of the kidney (MRTK) and a brain primitive neuroectodermal tumor (PNET). Genetic alterations of the SNF5/INI1/SMARCB1 gene were investigated by PCR-single-strand conformation polymorphism (SSCP), loss of heterozygosity (LOH), sequence, and karyotyping analyses, and the gene expression level was determined by real-time quantitative RT-PCR analysis. PCR band signals of each exon of the hSNF5/INI1 were weak or nearly undetectable in both MRTK and PNET, whereas those of the corresponding normal kidney were clearly detected. Aberrantly migrating SSCP bands led to identification of a nucleotide change in intron 8. Although this was regarded as a polymorphism, only the changed nucleotide was observed in the normal kidney of the patient. Allelic states in the parents were heterozygous for the polymorphism in the father and homozygous for the normal sequence in the mother. Thus, it was evident that a substantial genetic part of the maternal normal allele including SNF5/INI1 was deleted as a de novo germ-line mutation. In both tumors, LOH at microsatellite loci on the long arm of chromosome 22 was evident, and expression of SNF5/INI1 mRNA was drastically decreased compared to that in control tissues (0.7-3.9 vs. 123.6-153.5). Deletion of a substantial genetic part demonstrated in our patient is the novel appearance of a germ-line deletion of the SNF5/INI1 gene. Additional large somatic deletions resulted in total inactivation of the gene in both tumors. Our patient provides evidence for an important role of SNF5/INI1germ-line mutation in predisposing patients to multiple rhabdoid tumors.

Recent advances in pediatric renal neoplasia

Over the past 6 years, molecular genetic studies have significantly advanced our understanding of pediatric renal neoplasms. The cellular variant of congenital mesoblastic nephroma (but not the classic variant) has been shown to bear the same t(12;15)(p13;q25) and ETV6-NTRK3 gene fusion as infantile fibrosarcoma, a tumor with which it shares morphologic and clinical features. Rhabdoid tumor of the kidney is characterized by deletion of the hSNF5/INI1 gene, which links it to other rhabdoid tumors of infancy that arise in the soft tissue and brain. Primary renal synovial sarcomas and renal primitive neuroectodermal tumors have become accepted entities, and likely comprise a subset of what had previously been termed "adult Wilms tumor." Renal carcinomas associated with Xp11.2 translocations that result in fusions involving the TFE3 transcription factor gene have been delineated, including a distinctive neoplasm that shares the identical gene fusion as alveolar soft part sarcoma. Most recently, a distinctive type of renal neoplasm with a t(6;11)(p21;q12) has been described, and the cloning of the resulting gene fusion links it to the Xp11 translocation carcinomas. Together, these last two translocation-associated tumors represent a significant proportion of pediatric renal cell carcinomas. This review highlights each of these recent advances.

Molecular analysis of the rhabdoid predisposition syndrome in a child: a novel germline hSNF5/INI1 mutation and absence of c-myc amplification

The authors report a case of the rhabdoid predisposition syndrome (RPS) secondary to a germline hSNF5/INI1 mutation, whose brain tumor was originally unclassified but finally diagnosed as an atypical teratoid/rhabdoid tumor (AT/RT) by molecular analysis. A 7-month-old infant presented with hydrocephalus secondary to a huge pineal tumor and subsequently developed a renal rhabdoid tumor. The histology of the brain tumor was initially undetermined; however, an AT/RT was strongly suspected because of her clinical course. Mutational screening of the hSNF5/INI1 gene by heteroduplex and direct sequence analysis detected a missense mutation at codon 53 (CGA --> TGA, arginine --> stop) in both tumors, as well as in normal tissue of the kidney. Polymerase chain reaction (PCR)-based microsatellite analysis showed in both tumors allelic loss on chromosome arm 22q to which the hSNF5/INI1 gene maps. c-myc amplification was examined by differential PCR but not detected. Histologic review of the brain tumor by immunohistochemistry confirmed focal expression of epithelial membrane antigen and smooth muscle actin. These findings suggest that the brain tumor was really an AT/RT as a component of RPS secondary to a germline hSNF5/INI1 mutation. The present mutation has never been reported in the literature.

Genetic predisposition and screening in pediatric cancer

Pediatricians are often the health care providers who first detect the signs and symptoms of childhood cancer. Although pediatric malignancies are rare diseases, early diagnosis is an important factor leading to high cure rates of many types of cancers including retinoblastomara, Wilms' tumor, hepatoblastoma, rhabdomyosarcoma. thyroid carcinoma, and other solid tumors. A number of familial cancer syndromes present with childhood cancers that can be recognized or diagnosed by pediatricians. The genetic origins of several syndromes have been elucidated. Genetic testing is not yet available for all of these inherited cancers. A frequently updated list of genetic tests is available at www.genetests.org. The ordering and interpreting of genetic tests, however, is often best done by trained genetic counselors. The pediatrician will play a vital on-going role in following the at-risk child. In many of syndromes discussed, the cost effectiveness of the tests as well as that of any potential intervention needs further study. The role of the subtle genetic polymorphisms in pediatric tumorigenesis. many more of which will undoubtedly be described in the coming years, has not yet been translated into defined needs for interventions. Perhaps in the future it will be possible to understand the additive effect of multiple genetic polymorphisms and to determine genetic profiles of high cancer risk. Until suitable interventions are established, however, the study of genetic variability and cancer will await practical significance. Undoubtedly other major important cancer genes are yet to be discovered and characterized. An additional challenge is the counseling and management of children and adults who have a strong family history of cancer yet who do not have a recognizable syndrome. The role of the primary pediatrician is to recognize the major cancer genetic syndromes, to make appropriate referrals for genetic counseling and testing when indicated, and to ensure that adequate screening tests are being done.

A key role of the hSNF5/INI1 tumour suppressor in the control of the G1-S transition of the cell cycle

The hSNF5/INI1 gene encodes a member of the SWI/SNF chromatin remodelling complexes. It was recently identified as a tumour suppressor gene mutated in sporadic and hereditary Malignant Rhabdoid Tumours (MRT). However, the role of hSNF5/INI1 loss-of-function in tumour development is still unknown. Here, we show that the ectopic expression of wild-type hSNF5/INI1, but not that of truncated versions, leads to a cell cycle arrest by inhibiting the entry into S phase of MRT cells. This G1 arrest is associated with down-regulation of a subset of E2F targets including cyclin A, E2F1 and CDC6. This arrest can be reverted by coexpression of cyclin D1, cyclin E or viral E1A, whereas it cannot be counteracted by pRB-binding deficient E1A mutants. Moreover, hSNF5/INI1 is not able to arrest cells lacking a functional pRB. These observations suggest that the hSNF5/INI1-induced G1 arrest is dependent upon the presence of a functional pRB. However, the observation that a constitutively active pRB can efficiently arrest MRT cells indicates that hSNF5/INI1, at the difference of the ATPase subunits of the SWI/SNF complex, is dispensable for pRB function. Altogether, these data show that hSNF5/INI1 is a potent regulator of the entry into S phase, an effect that may account for its tumour suppressor role.

A single-nucleotide polymorphism of SMARCB1 in human breast cancers

The gene SMARCB1 has been considered a candidate for a tumor-suppressor gene. Nucleotide alterations in SMARCB1 have been reported, primarily in association with malignant rhabdoid tumor cases. We carried out a search for mutations in SMARCB1 in 60 human gastro-intestinal tract carcinoma cases, 122 breast cancer cases, and 36 human cancer cell lines. A single-nucleotide polymorphism (SNP) at codon 152 with an amino acid change (Asn to Asp) was found in 2 of 122 (1.6%) breast cancer cases, and another SNP at codon 299 without an amino acid change was found in tumor and normal tissues from 7 (5.7%) cases. Codons 152 and 299 of SMARCB1 are localized near or within the binding site for the cMYC protein. The amount of immunoprecipitated cMYC protein was reduced in two different cell lines expressing the codon 152 polymorphic SMARCB1 clone compared with those expressing wild-type SMARCB1, regardless of the identical expression of SMARCB1 protein in both cell lines. Therefore, the SNP at codon 152 is considered to be one of the coding SNPs that alters the SMARCB1-cMYC complex, which regulates various tumor-suppressor related genes against cancer. In addition, we identified three types of splicing isoforms, a 27-bp deleted gene, a 51-bp inserted gene, and a consensus gene, in both carcinoma tissues and in normal tissues; however, no clinical significance was observed for those isoforms. We found a nucleotide change at codon 152 of SMARCB1 that may alter the amount of immunoprecipitated cMYC protein, but we finally determined that SMARCB1 is highly conserved in human solid carcinomas.

Paediatric embryonic brain tumours. biological and clinical relevance of molecular genetic abnormalities

Embryonal tumours constitute the largest group of malignant paediatric brain tumours. Their origin and histological classification remain somewhat controversial. However, in recent years real progress has been made in our understanding of the molecular genetic abnormalities that govern the initiation and/or progression of these tumours. A number of these abnormalities appear to involve alterations in signalling systems that control normal cerebellar development. Increasing our understanding of both the biology and clinical relevance of these molecular defects is a major challenge to the field of paediatric neuro-oncology. However, it likely represents the only means by which we will advance the management of these tumours, significantly reducing disease-related morbidity and mortality. This review focuses on the principal molecular genetic abnormalities so far identified in embryonal brain tumours and discusses their biological and clinical relevance.

Haploinsufficiency of Snf5 (integrase interactor 1) predisposes to malignant rhabdoid tumors in mice

Malignant rhabdoid tumor (MRT) is an aggressive, highly lethal cancer of young children. Tumors occur in various locations, including kidney, brain, and soft tissues. Despite intensive therapy, 80% of affected children die, often within 1 year of diagnosis. The majority of MRT samples and cell lines have sustained biallelic inactivating mutations of the hSNF5 (integrase interactor 1) gene, suggesting that hSNF5 may act as a tumor suppressor. We sought to examine the role of Snf5 in development and cancer in a murine model. Here we report that Snf5 is widely expressed during embryogenesis with focal areas of high-level expression in the mandibular portion of the first branchial arch and central nervous system. Homozygous knockout of Snf5 results in embryonic lethality by embryonic day 7, whereas heterozygous mice are born at the expected frequency and appear normal. However, beginning as early as 5 weeks of age, heterozygous mice develop tumors consistent with MRT. The majority of tumors arise in soft tissues derived from the first branchial arch. Our findings constitute persuasive genetic evidence that Snf5, a core member of the Swi/Snf chromatin-remodeling complex, functions as a tumor suppressor gene, and, moreover, Snf5 heterozygotes provide a murine model of this lethal pediatric cancer.