Summary To establish whether loss of heterozygosity (LOH) for chromosome 16q in Wilms' tumours confers an adverse prognosis, DNA from 40 Wilms' tumour/normal pairs were analysed using highly polymorphic microsatellite markers along the length of 1 6q. Fifteen per cent of tumours showed LOH for 16q. Although the common region of allele loss spanned the 16q24-qter region, a second distinct region of LOH was identified in 16q21. (Coppes et al. 1992: Maw et al. 1992: Grundy et al. 1994: Austruy et al. 1995: Redeker et al 1996. Using a panel of informative markers for the region 16ql2.2-qter. Maw et al (1992) were the first to demonstrate LOH for 16q in 9 (20%c) of 45 informatiVe patients by Southem blot analysis. A larger follow--on study. as part of NWTS4. involving 232 patients. found a similar frequency of LOH at 17%7. but used only polymorphic markers that mapped to the distal 16q22-qter region (Grundv et al. 1994). In the study by Coppes et al (1992). using only two polymorphic markers mapping to 16q22.2 and 16q24.3. LOH was identified in 20% of tumours. The most recent studv. albeit in a relatively small group of patients (Austruy et al. 1995). found the highest level of LOH (25%7c) using a large panel of restriction length polymorphisms and microsatellite probes. Furthermore. LOH for 16q has been associated with a worse outcome because these patients have a relapse rate 3.3 times higher than those with tumours retaining heterozygosity for 16q (Grundy et al 1994).Because cytogenetic and molecular studies of Wilms' tumours clearly suggest a role for grenes on 16q in the molecular pathology of this tumour. we have undertaken LOH analysis for 16q markers using a large. well-characterized series of sporadic Wilms' tumours. Our results clearly show that LOH is relatively frequent in Wilms' tumours. especially in patients with an adverse outcome. MATERIALS AND METHODSDNA was prepared from tumour tissue and lymphocNies using standard phenol-chloroform extraction procedures described by Wadey et al (1990). The optimal polymerase chain reaction (PCR) conditions

Central nervous system primitive neuroectodermal tumours (CNS PNET) are high-grade, predominantly paediatric, brain tumours. Previously they have been grouped with medulloblastomas owing to their histological similarities. The WNT/b-catenin pathway has been implicated in many tumour types, including medulloblastoma. On pathway activation b-catenin (CTNNB1) translocates to the nucleus, where it induces transcription of target genes. It is commonly upregulated in tumours by mutations in the key pathway components APC and CTNNB1. WNT/b-catenin pathway status was investigated by immunohistochemical analysis of CTNNB1 and the pathway target cyclin D1 (CCND1) in 49 CNS PNETs and 46 medulloblastomas. The mutational status of APC and CTNNB1 (b-catenin) was investigated in 33 CNS PNETs and 22 medulloblastomas. CTNNB1 nuclear localisation was seen in 36% of CNS PNETs and 27% of medulloblastomas. A significant correlation was found between CTNNB1 nuclear localisation and CCND1 levels. Mutations in CTNNB1 were identified in 4% of CNS PNETs and 20% of medulloblastomas. No mutations were identified in APC. A potential link between the level of nuclear staining and a better prognosis was identified in the CNS PNETs, suggesting that the extent of pathway activation is linked to outcome. The results suggest that the WNT/b-catenin pathway plays an important role in the pathogenesis of CNS PNETs. However, activation is not caused by mutations in CTNNB1 or APC in the majority of CNS PNET cases.

Ependymomas encompass a heterogeneous group of central nervous system (CNS) neoplasms that occur along the entire neuroaxis. In recent years, extensive (epi-)genomic profiling efforts have identified several molecular groups of ependymoma that are characterized by distinct molecular alterations and/or patterns. Based on unsupervised visualization of a large cohort of genome-wide DNA methylation data, we identified a highly distinct group of pediatric-type tumors (n = 40) forming a cluster separate from all established CNS tumor types, of which a high proportion were histopathologically diagnosed as ependymoma. RNA sequencing revealed recurrent fusions involving the pleomorphic adenoma gene-like 1 (PLAGL1) gene in 19 of 20 of the samples analyzed, with the most common fusion being EWSR1:PLAGL1 (n = 13). Five tumors showed a PLAGL1:FOXO1 fusion and one a PLAGL1:EP300 fusion. High transcript levels of PLAGL1 were noted in these tumors, with concurrent overexpression of the imprinted genes H19 and IGF2, which are regulated by PLAGL1. Histopathological review of cases with sufficient material (n = 16) demonstrated a broad morphological spectrum of largely ependymoma-like tumors. Immunohistochemically, tumors were GFAP-positive and OLIG2- and SOX10-negative. In 3/16 of the cases, a dot-like positivity for EMA was detected. Consistent with other fusion-positive ependymal groups, all tumors in our series were located in the supratentorial compartment. Median age of the patients at the time of diagnosis was 6.2 years. Analysis of time to progression or recurrence revealed survival times comparable to those of patients with ZFTA:RELA-fused ependymoma. In summary, our findings suggest the existence of a novel group of supratentorial ependymomas that are characterized by recurrent PLAGL1 fusions and enriched for pediatric patients.