Perilobar nephrogenic rests are nonobligate molecular genetic precursor lesions of insulin-like growth factor-II-associated Wilms tumors

DROSHA Regulates Mesenchymal Gene Expression in Wilms Tumor

Wilms tumor, the most common pediatric kidney cancer, resembles embryonic renal progenitors. Currently, there are no ways to therapeutically target Wilms tumor driver mutations, such as in the microRNA processing gene DROSHA. In this study, we used a "multiomics" approach to define the effects of DROSHA mutation in Wilms tumor. We categorized Wilms tumor mutations into four mutational subclasses with unique transcriptional effects: microRNA processing, MYCN activation, chromatin remodeling, and kidney developmental factors. In particular, we find that DROSHA mutations are correlated with de-repressing microRNA target genes that regulate differentiation and proliferation and a self-renewing, mesenchymal state. We model these findings by inhibiting DROSHA expression in a Wilms tumor cell line, which led to upregulation of the cell cycle regulator cyclin D2 (CCND2). Furthermore, we observed that DROSHA mutations in Wilms tumor and DROSHA silencing in vitro were associated with a mesenchymal state with aberrations in redox metabolism. Accordingly, we demonstrate that Wilms tumor cells lacking microRNAs are sensitized to ferroptotic cell death through inhibition of glutathione peroxidase 4, the enzyme that detoxifies lipid peroxides. Implications: This study reveals genotype-transcriptome relationships in Wilms tumor and points to ferroptosis as a potentially therapeutic vulnerability in one subset of Wilms tumor.

Hallmark discoveries in the biology of Wilms tumour

The modern study of Wilms tumour was prompted nearly 50 years ago, when Alfred Knudson proposed the 'two-hit' model of tumour development. Since then, the efforts of researchers worldwide have substantially expanded our knowledge of Wilms tumour biology, including major advances in genetics - from cloning the first Wilms tumour gene to high-throughput studies that have revealed the genetic landscape of this tumour. These discoveries improve understanding of the embryonal origin of Wilms tumour, familial occurrences and associated syndromic conditions. Many efforts have been made to find and clinically apply prognostic biomarkers to Wilms tumour, for which outcomes are generally favourable, but treatment of some affected individuals remains challenging. Challenges are also posed by the intratumoural heterogeneity of biomarkers. Furthermore, preclinical models of Wilms tumour, from cell lines to organoid cultures, have evolved. Despite these many achievements, much still remains to be discovered: further molecular understanding of relapse in Wilms tumour and of the multiple origins of bilateral Wilms tumour are two examples of areas under active investigation. International collaboration, especially when large tumour series are required to obtain robust data, will help to answer some of the remaining unresolved questions.

Germline (epi)genetics reveals high predisposition in females: a 5-year, nationwide, prospective Wilms tumour cohort

BACKGROUND

Studies suggest that Wilms tumours (WT) are caused by underlying genetic (5%-10%) and epigenetic (2%-29%) mechanisms, yet studies covering both aspects are sparse.

METHODS

We performed prospective whole-genome sequencing of germline DNA in Danish children diagnosed with WT from 2016 to 2021, and linked genotypes to deep phenotypes.

RESULTS

Of 24 patients (58% female), 3 (13%, all female) harboured pathogenic germline variants in WT risk genes (FBXW7, WT1 and REST). Only one patient had a family history of WT (3 cases), segregating with the REST variant. Epigenetic testing revealed one (4%) additional patient (female) with uniparental disomy of chromosome 11 and Beckwith-Wiedemann syndrome (BWS). We observed a tendency of higher methylation of the BWS-related imprinting centre 1 in patients with WT than in healthy controls. Three patients (13%, all female) with bilateral tumours and/or features of BWS had higher birth weights (4780 g vs 3575 g; p=0.002). We observed more patients with macrosomia (>4250 g, n=5, all female) than expected (OR 9.98 (95% CI 2.56 to 34.66)). Genes involved in early kidney development were enriched in our constrained gene analysis, including both known (WT1, FBXW7) and candidate (CTNND1, FRMD4A) WT predisposition genes. WT predisposing variants, BWS and/or macrosomia (n=8, all female) were more common in female patients than male patients (p=0.01).

CONCLUSION

We find that most females (57%) and 33% of all patients with WT had either a genetic or another indicator of WT predisposition. This emphasises the need for scrutiny when diagnosing patients with WT, as early detection of underlying predisposition may impact treatment, follow-up and genetic counselling.

Somatic, Genetic and Epigenetic Changes in Nephrogenic Rests and Their Role in the Transformation to Wilms Tumors, a Systematic Review

OBJECTIVE

To review somatic genetic changes in nephrogenic rests (NR), which are considered to be precursor lesions of Wilms tumors (WT).

METHODS

This systematic review is written according to the PRISMA statement. PubMed and EMBASE were systematically searched for articles in the English language studying somatic genetic changes in NR between 1990 and 2022.

RESULTS

Twenty-three studies were included in this review, describing 221 NR of which 119 were pairs of NR and WT. Single gene studies showed mutations in WT1 and WTX, but not CTNNB1 to occur in both NR and WT. Studies investigating chromosomal changes showed loss of heterozygosity of 11p13 and 11p15 to occur in both NR and WT, but loss of 7p and 16q occurred in WT only. Methylome-based studies found differential methylation patterns between NR, WT, and normal kidney (NK).

CONCLUSIONS

Over a 30-year time frame, few studies have addressed genetic changes in NR, likely hampered by technical and practical limitations. A limited number of genes and chromosomal regions have been implicated in the early pathogenesis of WT, exemplified by their occurrence in NR, including WT1, WTX, and genes located at 11p15. Further studies of NR and corresponding WT are urgently needed.

Nephrogenic rest vs immature teratoma associated with lumbosacral lipomyelomeningocele: a case report and review of the literature

BACKGROUND

Lipomyelomeningoceles (LMMs) are subcutaneous lipomas with dural penetration that often present with spinal cord tethering and may lead to neurological deterioration if untreated. This report describes a rare case of an LMM associated with immature nephroblastic tissue, representing a nephrogenic rest (NR) or, less likely, an immature teratoma.

CLINICAL PRESENTATION

An 8-day-old infant girl presented to the clinic with a sacral dimple. Imaging demonstrated a tethered spinal cord with low-lying conus medullaris and an LMM. A firm mass was noted in the subcutaneous lipoma. Detethering surgery and removal of the lipoma and mass were performed at the age of 6 months. Pathological examination identified the mass as cartilage, fat, and immature nephroblastic tissue consistent with NR tissue or, less likely, a teratoma with renal differentiation.

CONCLUSION

This presentation of an LMM associated with an immature teratoma or NR poses a risk of malignant transformation in patients. As a result, careful surgical dissection, resection, and close clinical follow-up are recommended for these patients.

WILMS TUMOR MUTATIONAL SUBCLASSES CONVERGE TO DRIVE CCND2 OVEREXPRESSION

Wilms tumor, the most common kidney cancer in pediatrics, arises from embryonic renal progenitors. Although many patients are cured with multimodal therapy, outcomes remain poor for those with high-risk features. Recent sequencing efforts have provided few biological or clinically actionable insights. Here, we performed DNA and RNA sequencing on 94 Wilms tumors to understand how Wilms tumor mutations transform the transcriptome to arrest differentiation and drive proliferation. We show that most Wilms tumor mutations fall into four classes, each with unique transcriptional signatures: microRNA processing, MYCN activation, chromatin remodeling, and kidney development. In particular, the microRNA processing enzyme DROSHA is one of the most commonly mutated genes in Wilms tumor. We show that DROSHA mutations impair pri-microRNA cleavage, de-repress microRNA target genes, halt differentiation, and overexpress cyclin D2 (CCND2). Several mutational classes converge to drive CCND2 overexpression, which could render them susceptible to cell-cycle inhibitors.

Tumor biology, biomarkers, and liquid biopsy in pediatric renal tumors

The expansion of knowledge regarding driver mutations for Wilms tumor (WT) and malignant rhabdoid tumor of the kidney (MRT) and various translocations for other pediatric renal tumors opens up new possibilities for diagnosis and treatment. In addition, there are growing data surrounding prognostic factors that can be used to stratify WT treatment to improve outcomes. Here, we review the molecular landscape of WT and other pediatric renal tumors as well as WT prognostic factors. We also review incorporation of circulating tumor DNA/liquid biopsies to leverage this molecular landscape, with potential use in the future for distinguishing renal tumors at the time of diagnosis and elucidating intratumor heterogeneity, which is not well evaluated with standard biopsies. Incorporation of liquid biopsies will require longitudinal collection of multiple biospecimens. Further preclinical research, identification and validation of biomarkers, molecular studies, and data sharing among investigators are crucial to inform therapeutic strategies that improve patient outcomes.

Wilms tumour

Wilms tumour (WT) is a childhood embryonal tumour that is paradigmatic of the intersection between disrupted organogenesis and tumorigenesis. Many WT genes play a critical (non-redundant) role in early nephrogenesis. Improving patient outcomes requires advances in understanding and targeting of the multiple genes and cellular control pathways now identified as active in WT development. Decades of clinical and basic research have helped to gradually optimize clinical care. Curative therapy is achievable in 90% of affected children, even those with disseminated disease, yet survival disparities within and between countries exist and deserve commitment to change. Updated epidemiological studies have also provided novel insights into global incidence variations. Introduction of biology-driven approaches to risk stratification and new drug development has been slower in WT than in other childhood tumours. Current prognostic classification for children with WT is grounded in clinical and pathological findings and in dedicated protocols on molecular alterations. Treatment includes conventional cytotoxic chemotherapy and surgery, and radiation therapy in some cases. Advanced imaging to capture tumour composition, optimizing irradiation techniques to reduce target volumes, and evaluation of newer surgical procedures are key areas for future research.

MiR-155-5p exerts tumor-suppressing functions in Wilms tumor by targeting IGF2 via the PI3K signaling pathway

BACKGROUND

MicroRNA-155-5p (miR-155-5p) has been reported to play an oncogenic role in different human malignancies; however, its role in Wilms tumor (WT) remains unclear.

METHODS

Differentially expressed miRNAs (DE-miRNAs) and mRNAs (DEGs) in WT blood and tissues were identified by using miRNA microarray and RNA-sequencing. Bioinformatics prediction and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses were used to predict the potential functions of DE-miRNAs. DE-miRNAs and DEGs in WT obtained from Gene Expression Omnibus (GEO) and Therapeutically Applicable Research to Generate Effective Treatments (TARGET) were identified by using the "edgeR" package. RT-qPCR was used to explore miR-155-5p and IGF2 expression and their clinical significance in WT specimens. A rhabdoid cell line (G401) and Ewing sarcoma cell line (SK-NEP-1) were used. Immunohistochemical staining, western blotting and dual-luciferase reporter assays were performed to study the mechanisms involved. The CCK-8, flow cytometry, wound healing and transwell assays were performed to identify the effects of miR-155-5p and IGF2 knockdown on cell proliferation, apoptosis, migration and invasion, respectively.

RESULTS

MiR-155-5p was downregulated in both blood and tissues from WT patients who did not receive chemotherapy before surgery but was upregulated in tissues from WT patients who had received chemotherapy before surgery. IGF2, PI3K, AKT and mTOR were found to be upregulated in WT tissues. Additionally, miR-155-5p and IGF2 were significantly correlated with TNM stage and lymphatic metastasis in WT patients. Molecular mechanism exploration indicated that IGF2 was downregulated by miR-155-5p via direct binding to its 3' untranslated region in cell lines. Furthermore, IGF2, PI3K, AKT and mTOR expression was inversely correlated with miR-155-5p expression, and PI3K, AKT and mTOR expression was positively correlated with IGF2 expression in cell culture. Functional studies demonstrated that miR-155-5p upregulation and IGF2 knockdown suppressed cell proliferation, migration and invasion and induced cell apoptosis. Moreover, the tumor-suppressing effects of miR-155-5p in cells were abrogated by miR-155-5p inhibitor treatment.

CONCLUSIONS

Taken together, these findings suggest that miR-155-5p functions as a tumor suppressor in WT through inactivating the PI3K/AKT/mTOR signaling pathway by directly targeting IGF2. Thus, miR-155-5p might be a novel therapeutic target for WT.

Lin28 and let-7 regulate the timing of cessation of murine nephrogenesis

In humans and in mice the formation of nephrons during embryonic development reaches completion near the end of gestation, after which no new nephrons are formed. The final nephron complement can vary 10-fold, with reduced nephron number predisposing individuals to hypertension, renal, and cardiovascular diseases in later life. While the heterochronic genes lin28 and let-7 are well-established regulators of developmental timing in invertebrates, their role in mammalian organogenesis is not fully understood. Here we report that the Lin28b/let-7 axis controls the duration of kidney development in mice. Suppression of let-7 miRNAs, directly or via the transient overexpression of LIN28B, can prolong nephrogenesis and enhance kidney function potentially via upregulation of the Igf2/H19 locus. In contrast, kidney-specific loss of Lin28b impairs renal development. Our study reveals mechanisms regulating persistence of nephrogenic mesenchyme and provides a rationale for therapies aimed at increasing nephron mass.

Nephrogenesis ceases after postnatal day 2 in the mouse or after the 36th week of gestation in humans, but how this is regulated is unclear. Here, the authors identify a role for the RNA-binding protein Lin28 and suppression of let-7 microRNA in regulating the duration of nephrogenesis.

The first investigation of Wilms' tumour atomic structure-nitrogen and carbon isotopic composition as a novel biomarker for the most individual approach in cancer disease

The paper describes a novel approach to investigating Wilms' tumour (nephroblastoma) biology at the atomic level. Isotope Ratio Mass Spectrometry (IRMS) was used to directly assess the isotope ratios of nitrogen and carbon in 84 Wilms' tumour tissue samples from 28 cases representing the histological spectrum of nephroblastoma. Marked differences in nitrogen and carbon isotope ratios were found between nephroblastoma histological types and along the course of cancer disease, with a breakout in isotope ratio of the examined elements in tumour tissue found between stages 2 and 3. Different isotopic compositions with regard to nitrogen and carbon content were observed in blastemal Wilms' tumour, with and without focal anaplasia, and in poorly- and well-differentiated epithelial nephroblastoma. This first assessment of nitrogen and carbon isotope ratio reveals the previously unknown part of Wilms' tumour biology and represents a potential novel biomarker, allowing for a highly individual approach to treating cancer. Furthermore, this method of estimating isotopic composition appears to be the most sensitive tool yet for cancer tissue evaluation, and a valuable complement to established cancer study methods with prospective clinical impact.

Nephrogenic rests in Wilms tumors treated with preoperative chemotherapy: The UK SIOP Wilms Tumor 2001 Trial experience

BACKGROUND

Nephrogenic rests (NRs) are abnormally persistent foci of embryonal cells, thought to be the precursor lesion of Wilms tumors (WTs). To date, their presence has not been systematically examined in WTs treated with preoperative chemotherapy.

METHODS

A systematic analysis of the data on NRs in WTs treated with preoperative chemotherapy obtained from the UK cohort of the International Society of Pediatric Oncology (SIOP) WT 2001 Trial. The study was based on central pathology review of full sets of slides from pathological specimens, with a median of 28 slides reviewed per case.

RESULTS

NRs were identified in 40% of unilateral WTs, including 25% perilobar nephrogenic rest (PLNR), 9% intralobar nephrogenic rest (ILNR), 5% both PLNR and ILNR, and 1% nephroblastomatosis, and in 93% of cases with bilateral lesions. ILNRs were associated with stromal histology and a younger age at diagnosis and found frequently in patients with congenital anomalies associated with WT1 mutation. PLNRs were found frequently in patients with overgrowth syndromes.

CONCLUSIONS

The prevalence of NRs in WTs after preoperative chemotherapy observed in SIOP UK WT 2001 Trial is similar to the previously published data on NRs not treated with preoperative chemotherapy. Their epidemiology supports at least two pathways to Wilms tumorigenesis.

Bilateral Wilms tumour: a review of clinical and molecular features

Wilms tumour (WT) is the most common paediatric kidney cancer and affects approximately one in 10 000 children. The tumour is associated with undifferentiated embryonic lesions called nephrogenic rests (NRs) or, when diffuse, nephroblastomatosis. WT or NRs can occur in both kidneys, termed bilateral disease, found in only 5-8% of cases. Management of bilateral WT presents a major clinical challenge in terms of maximising survival, preserving renal function and understanding underlying genetic risk. In this review, we compile clinical data from 545 published cases of bilateral WT and discuss recent progress in understanding the molecular basis of bilateral WT and its associated precursor NRs in the context of the latest radiological, surgical and epidemiological features.

Constitutional de novo deletion of the FBXW7 gene in a patient with focal segmental glomerulosclerosis and multiple primitive tumors

Multiple primary malignant neoplasms are rare entities in the clinical setting, but represent an important issue in the clinical management of patients since they could be expression of a genetic predisposition to malignancy. A high resolution genome wide array CGH led us to identify the first case of a de novo constitutional deletion confined to the FBXW7 gene, a well known tumor suppressor, in a patient with a syndromic phenotype characterized by focal segmental glomerulosclerosis and multiple primary early/atypical onset tumors, including Hodgkin's lymphoma, Wilms tumor and breast cancer. Other genetic defects may be associated with patient's phenotype. In this light, constitutional mutations at BRCA1, BRCA2, TP53, PALB2 and WT1 genes were excluded by performing sequencing and MLPA analysis; similarly, we ruled out constitutional abnormalities at the imprinted 11p15 region by methylation specific -MLPA assay. Our observations sustain the role of FBXW7 as cancer predisposition gene and expand the spectrum of its possible associated diseases.

Comparative methylome analysis identifies new tumour subtypes and biomarkers for transformation of nephrogenic rests into Wilms tumour

BACKGROUND

Wilms tumours (WTs) are characterised by several hallmarks that suggest epimutations such as aberrant DNA methylation are involved in tumour progression: loss of imprinting at 11p15, lack of recurrent mutations and formation of nephrogenic rests (NRs), which are lesions of retained undifferentiated embryonic tissue that can give rise to WTs.

METHODS

To identify such epimutations, we performed a comprehensive methylome analysis on 20 matched trios of micro-dissected WTs, NRs and surrounding normal kidneys (NKs) using Illumina Infinium HumanMethylation450 Bead Chips and functionally validated findings using RNA sequencing.

RESULTS

Comparison of NRs with NK revealed prominent tissue biomarkers: 629 differentially methylated regions, of which 55% were hypermethylated and enriched for domains that are bivalent in embryonic stem cells and for genes expressed during development (P = 2.49 × 10(-5)). Comparison of WTs with NRs revealed two WT subgroups; group-2 WTs and NRs were epigenetically indistinguishable whereas group-1 WTs showed an increase in methylation variability, hypomethylation of renal development genes, hypermethylation and relative loss of expression of cell adhesion genes and known and potential new WT tumour suppressor genes (CASP8, H19, MIR195, RB1 and TSPAN32) and was strongly associated with bilateral disease (P = 0.032). Comparison of WTs and NRs to embryonic kidney highlighted the significance of polycomb target methylation in Wilms tumourigenesis.

CONCLUSIONS

Methylation levels vary during cancer evolution. We have described biomarkers related to WT evolution from its precursor NRs which may be useful to differentiate between these tissues for patients with bilateral disease.

The IGF signalling pathway in Wilms tumours--a report from the ENCCA Renal Tumours Biology-driven drug development workshop

It is hypothesised that Wilms tumour (WT) results from aberrant renal development due to its embryonic morphology, associated undifferentiated precursor lesions (termed nephrogenic rests) and embryonic kidney-like chromatin and gene expression profiles. From the study of overgrowth syndrome-associated WT, germline dysregulation was identified in the imprinted region at 11p15 affecting imprinted genes IGF2 and H19. This is also detected in ~70% sporadic cases, making this the most common somatic molecular aberration in WT. This review summarises the critical discussion at an international workshop held under the auspices of The European Network for Cancer Research in Children and Adolescents (ENCCA) consortium, where the potential for drug development to target IGF2 and the WT epigenome was debated. Here, we consider current cancer treatments which include targeting the IGF pathway and the use of methylation agents alone or in combination with other drugs in clinical trials of paediatric cancers. Finally, we discuss the possibility of the use of these drugs to treat patients with WT.

Molecular characterization of Wilms' tumor from a resource-constrained region of sub-Saharan Africa

Sub-Saharan African children have an increased incidence of Wilms' tumor (WT) and experience alarmingly poor outcomes. Although these outcomes are largely due to inadequate therapy, we hypothesized that WT from this region exhibits features of biological aggressiveness that may warrant broader implementation of high-risk therapeutic protocols. We evaluated 15 Kenyan WT (KWT) for features of aggressive disease (blastemal predominance and Ki67/cellular proliferation) and treatment resistance (anaplasia and p53 immunopositivity). To explore the additional biological features of KWT, we determined the mutational status of the CTNNB1/β-catenin and WT1 genes and performed immunostaining for markers of Wnt pathway activation (β-catenin) and nephronic progenitor cell self-renewal (WT1, CITED1 and SIX2). We characterized the proteome of KWT using imaging mass spectrometry (IMS). The results were compared to histology- and age-matched North American WT (NAWT) controls. For patients with KWT, blastemal predominance was noted in 53.3% and anaplasia in 13%. We detected increased loss to follow-up (p = 0.028), disease relapse (p = 0.044), mortality (p = 0.001) and nuclear unrest (p = 0.001) in patients with KWT compared to controls. KWT and NAWT showed similar Ki67/cellular proliferation. We detected an increased proportion of epithelial nuclear β-catenin in KWT (p = 0.013). All 15 KWT specimens were found to harbor wild-type CTNNB1/β-catenin, and one contained a WT1 nonsense mutation. WT1 was detected by immunostaining in 100% of KWT, CITED1 in 80% and SIX2 in 80%. IMS revealed a molecular signature unique to KWT that was distinct from NAWT. The African WT specimens appear to express markers of adverse clinical behavior and treatment resistance and may require alternative therapies or implementation of high-risk treatment protocols.

Perilobar nephrogenic rests and chromosome 22

Perilobar nephrogenic rests (NR) are precursor lesions that may display genetic changes similar to their associated Wilms tumor (WT). Two patients presented with WT, both with perilobar NR and 1 with bilateral, multifocal metachronous WT. Both patients' WT displayed monosomy 22 as the predominant cytogenetic change, and the constitutional cytogenetic analysis was normal. The purpose of our study was to identify at what stage in the morphologic progression from NR to WT the monosomy 22 occurred by using a fluorescent in situ hybridization probe for chromosome 22 in the subtypes of perilobar NR and WT present in both cases. Section and core fluorescent in situ hybridization with a chromosome 22 probe was performed on formalin-fixed, paraffin-embedded tissues containing WT and perilobar NR. We also performed fluorescent-based microsatellite analysis on some of the WT in the bilateral case to determine whether there was a preferential loss of the same allele of chromosome 22. Sclerotic and dormant perilobar NR showed a rate of monosomy 22 of only approximately 30%, but this increased to approximately 50% in hyperplastic and adenomatous NR. Monosomy 22 was present in 60%-80% of nuclei in WT. Microsatellite analysis showed loss of homozygosity, with preferential loss of the same allele of chromosome 22 in the tumors examined. There are differences in the rate of detection of monosomy 22 in perilobar NR and WT, suggesting loss of chromosome 22 in the progression of perilobar NR to WT in a subset of tumors.

Pathology, genetics and cytogenetics of Wilms' tumour

Wilms' tumour (WT) is an embryonal cancer of childhood and is thought to be derived from embryonic kidney precursor cells. The Knudson two hit model was initially thought to occur in WT, but findings emerging from genetic and cytogenetic studies in the past two decades have implicated several genetic events. Recent techniques in genetic analysis have improved our ability to characterise changes in genes involved in WT which include WT1, CTNNB1, IGF2 and WTX. These genetic events have not only provided insight into the pathobiology of this malignancy, but the recognition of these candidate genes may offer potential targets for novel therapies. In this review, we will provide an overview of the pathological, genetic and cytogenetic characteristics of WT.

Loss of imprinting of IGF2 and the epigenetic progenitor model of cancer

Among the hypotheses discussing cancer formation, the cancer stem cell (CSC) theory is one receiving widespread support. One version of this theory states that changes in otherwise healthy cells can cause formation of tumor- initiating cells (TICs), which have the potential to create precancerous stem cells that can lead to CSC formation. These CSCs can be rare, in contrast to their differentiated progeny, which give rise to the vast majority of the tumor mass in most cancers. Loss of imprinting (LOI) of the insulin-like growth factor-2 (IGF2) gene is one change that can produce these TICs via an epigenetic progenitor model of tumorigenesis. While IGF2 usually supports normal cellular growth, LOI of IGF2 may lead to overexpression of the gene and moreover global chromatin instability. This modification has been observed in many forms of cancer, and given the effect of LOI of IGF2 and its role in cancer, detecting a loss of imprinting in this gene could serve as a valuable diagnostic tool. Preclinical data has shown some progress in identifying therapeutic approaches seeking to exploit this relationship. Thus, further research surrounding LOI of IGF2 could lead to increased understanding of several cancer types and enhance therapies against these diseases.

Detection of chromosome copy number alterations in metanephric adenomas by array comparative genomic hybridization

Metanephric adenoma is a rare benign renal tumor typically found in adults. Previous cytogenetic analyses, including karyotyping, fluorescence in situ hybridization (FISH), and comparative genomic hybridization, have yielded conflicting results regarding the somatic genetic aberrations of these tumors. In this study, we investigated the genomic profile of nine cases of metanephric adenoma using array comparative genomic hybridization. Two cases revealed multiple chromosomal gains and losses. Three cases showed sporadic chromosomal imbalances involving no more than three chromosomes. Four cases showed normal chromosome copy numbers. The gain of chromosome 19 was the most common finding (five cases), and FISH using 19p and 19q telomeric probes further confirmed this finding. We did not observe consistent gains of chromosomes 7 and 17, which are common in papillary renal cell carcinoma, neither did we find chromosomal alterations frequently present in Wilms' tumors, including chromosome gains of 1q, 7q, and 12, and losses of 11p and 16q. Our series demonstrates that the genetic profile of metanephric adenoma is fundamentally distinct from those of papillary renal cell carcinoma and Wilms' tumor.

Deletions of 16q in Wilms tumors localize to blastemal-anaplastic cells and are associated with reduced expression of the IRXB renal tubulogenesis gene cluster

Wilms tumor is the most common pediatric renal neoplasm, but few molecular prognostic markers have been identified for this tumor. Somatic deletion in the long arm of chromosome 16 (16q) is known to predict a less favorable outcome in Wilms tumor, but the underlying molecular mechanisms are not known. We show that 16q deletions are typically confined to immature anaplastic-blastic tumor elements, while deletions are absent in maturing tumor components. The smallest region of deletion overlap mapped to a 1.8-Mb segment containing the IRXB gene cluster including IRX3, IRX5, and IRX6, of which IRX3 is a recently identified regulator of tubular maturation during nephrogenesis. Tumors with 16q deletion showed a lower overall mRNA expression of IRXB genes, and 16q-deleted tumor cells failed to express IRX3 while it was expressed in differentiating tubular tumor elements with intact 16q. Consistent with a role for IRX3 in tubular differentiation, gene sets linked to Notch signaling, Rho signaling, and ion channel activity were enriched in tumors with high IRX3 expression, while WTs with low expression were enriched for gene sets linked to cell cycle progression. Low mRNA levels of IRXB genes were associated with diffuse anaplasia, high-stage disease, and death. A disturbed balance between tubular differentiation and self-renewal of anaplastic-blastic elements may thus be one mechanism linking 16q deletion to adverse outcome in Wilms tumor.

A distinct spectrum of copy number aberrations in pediatric high-grade gliomas

PURPOSE

As genome-scale technologies begin to unravel the complexity of the equivalent tumors in adults, we can attempt detailed characterization of high-grade gliomas in children, that have until recently been lacking. Toward this end, we sought to validate and extend investigations of the differences between pediatric and adult tumors.

EXPERIMENTAL DESIGN

We carried out copy number profiling by array comparative genomic hybridization using a 32K bacterial artificial chromosome platform on 63 formalin-fixed paraffin-embedded cases of high-grade glioma arising in children and young people (<23 years).

RESULTS

The genomic profiles of these tumors could be subclassified into four categories: those with stable genomes, which were associated with a better prognosis; those with aneuploid and those with highly rearranged genomes; and those with an amplifier genotype, which had a significantly worse clinical outcome. Independent of this was a clear segregation of cases with 1q gain (more common in children) from those with concurrent 7 gain/10q loss (a defining feature of adults). Detailed mapping of all the amplification and deletion events revealed numerous low-frequency amplifications, including IGF1R, PDGFRB, PIK3CA, CDK6, CCND1, and CCNE1, and novel homozygous deletions encompassing unknown genes, including those at 5q35, 10q25, and 22q13. Despite this, aberrations targeting the "core signaling pathways" in adult glioblastomas are significantly underrepresented in the pediatric setting.

CONCLUSIONS

These data highlight that although there are overlaps in the genomic events driving gliomagenesis of all ages, the pediatric disease harbors a distinct spectrum of copy number aberrations compared with adults.

Two candidate tumor suppressor genes, MEOX2 and SOSTDC1, identified in a 7p21 homozygous deletion region in a Wilms tumor

A SNP-based array analysis of 100 Wilms tumors (WT) from 97 patients identified 7p alterations (hemizygous and homozygous deletions and uniparental disomy) in nine tumors. The homozygous deletion (HD) region of 7p21 found in one tumor partially overlapped with another HD region reported previously, and was narrowed down to a 2.1-Mb region. Based on an expression analysis of 10 genes located in the HD region in 3 WT lines and previous studies on tumorigenic roles of MEOX2 and SOSTDC1, we further analyzed these two genes. Sequencing showed no mutation in MEOX2, but two missense mutations (L50F and Q129L) in SOSTDC1 in four tumors; L50F in two tumors was of germline origin. Expression levels (0, 1+ and 2+) of MEOX2 were lower in four tumors with 7p alterations than in 18 tumors with no 7p alterations (P = 0.017), and those of SOSTDC1 tended to be lower in five tumors with 7p alterations or SOSTDC1 mutation than in 17 tumors with no 7p alterations or SOSTDC1 mutation (P = 0.056). There were no significant differences in clinical characteristics between nine patients with 7p alterations and 88 patients with no 7p alterations; however, there was a difference in the status of IGF2 (uniparental disomy, loss of imprinting, or retention of imprinting) between the two patient groups (P = 0.028). Losses of MEOX2 and SOSTDC1 may accelerate angiogenesis and augment signals in the Wnt pathway, respectively. Both genes may be prime candidates for 7p tumor suppressor genes, which may have a role in the progression of Wilms tumorigenesis.

Pediatric genitourinary tumors

PURPOSE OF REVIEW

We will review the 2007/2008 literature on pediatric genitourinary tumors.

RECENT FINDINGS

Newly identified constitutional epigenetic defects in Wilms tumor genes extend the understanding of Wilms tumor risk in children lacking syndromic features, and add to the complexity of the pathogenesis of these tumor suppressor genes. Pediatric renal cell carcinoma has distinct molecular characteristics and clinical associations from the adult counterpart. The pathway from PAX3-FKHR translocation to the development of rhabdomyosarcoma tumors has been further elucidated.

SUMMARY

Therapeutic strategies continue to be driven by developments in molecular diagnostics in pediatric genitourinary tumors.

Expression of hepatocyte growth factor and its receptor met in Wilms' tumors and nephrogenic rests reflects their roles in kidney development

PURPOSE

Hepatocyte growth factor (HGF) and its receptor Met are known to play diverse roles in both organogenesis and cancer. Wilms' tumor (WT) is a prototype for the link between abrogated development and neoplasia, with dysregulation of growth factor/receptor pathways playing key roles. Despite this, an understanding of the HGF/Met axis in the process is lacking.

EXPERIMENTAL DESIGN

Observing copy number alterations at the loci for these genes in WTs and their precursor lesions nephrogenic rests, we examined protein expression by immunohistochemistry and investigated the effects of HGF on an in vitro model of kidney development.

RESULTS

HGF was preferentially expressed in the blastemal cells of nephrogenic rests but not WTs. Met expression was infrequent and restricted to well-differentiated epithelial cells and stroma in both lesions. In an independent cohort of favorable histology WTs on a tissue microarray, HGF was expressed in 15 of 193 (8%) cases and correlated with a predominance of epithelial cells, whereas Met expression was observed in 25 of 179 (14%) cases and was associated with stromal subtypes. In a mouse mesonephric cell line model, we observed Met expression in culture conditions reflecting both mesenchymal and epithelial differentiation, whereas HGF was up-regulated in association with acquisition of a more epithelial-like phenotype. This could be mimicked by exogenous exposure of mesenchymal-like cells to recombinant HGF.

CONCLUSIONS

These data show that the relatively infrequent expression of HGF and Met in WT tumorigenesis reflects their roles in nephrogenesis, particularly the mesenchymal-to-epithelial transition, rather than a dependence on oncogenic signaling pathways.