Multilocus loss of heterozygosity allelotypes identify a genetic pathway associated with progression from low to high stage disease in neuroblastoma.

Neuroblastoma is a heterogeneous tumour with a variety of clinical phenotypes, ranging from a localised tumour with excellent outcome (stage 1) to a metastatic, usually fatal malignancy (stage 4). In order to investigate the genetic relationship between these tumour subtypes, a loss of heterozygosity (LOH) analysis was carried out. Composite LOH allelotypes incorporating data from 96 loci on 5 chromosomes (1p, 3p, 4p, 11q, 14q), were constructed for 62 neuroblastomas. Neuroblastomas with similar allelotypes were clustered into groups and allelotype patterns correlated with clinical features. Three distinct genetic subgroups of neuroblastoma were observed. The largest group (50% of tumours) was characterised by specific allelotype patterns indicative of a stepwise accumulation of genetic alterations (11q LOH-->1p, 4p, and/or 14q LOH-->3p LOH), associated with progression from low to high stage disease. These tumours are distinct from MYCN amplified neuroblastomas which have a more rapid and aggressive disease course, and also a proportion of low stage tumours, often ganglioneuromas or ganglioneuroblastomas, with restricted growth potential.

The Wnt antagonist sFRP1 in colorectal tumorigenesis.

Regions of the short arm of chromosome 8 are deleted frequently in a range of solid tumors, indicating that tumor suppressor genes reside at these loci. In this study, we have examined the properties of the Wnt signaling antagonist secreted frizzled-related protein (sFRP) 1 as a candidate for this role at c8p11.2. An initial survey of 10 colorectal tumors, selected by the presence of isolated short deletions of the 8p11.2 region, identified three chain-terminating mutations, all within the first exon, which encodes the cysteine-rich domain. None of these tumors exhibited microsatellite instability, indicating intact mismatch repair gene function. The preserved sFRP1 alleles in the remaining seven tumors each contained a polymorphic three-base insertion in the signal sequence, but in a broader study, no association was found between this and the development of colorectal cancer. Epigenetic inhibition of sFRP1 transcription was investigated, and increased methylation of the promotor region was demonstrated in an additional cohort of 51 locally advanced colorectal cancers. Hypermethylation was identified in 40 of 49 (82%) cancers and in only 11 of 36 (30%) matched normal mucosal samples (P < 0.001). Semiquantitative analysis, by real-time PCR, of mRNA expression in 37 of the same cohort of 51 cancers revealed that sFRP1 mRNA expression was down-regulated in 28 (76%) cases compared with matched normal large bowel mucosa. The 3' end of the sFRP1 mRNA also was found to be alternatively spliced, compared with the prototype liver and lung forms, in the colon and a number of other tissues, yielding an extended COOH terminus, which may influence its activity in a tissue-specific manner. The inactivation and down-regulation of sFRP1 observed are consistent with it acting as a tumor suppressor gene in colorectal carcinogenesis. Because beta-catenin is constitutively active in the majority of colorectal tumors, it is unlikely that sFRP1 can act in the canonical Wnt response pathway. Therefore, we propose that the reduced activity or absence of sFRP1 allows the transduction of noncanonical Wnt signals, which contribute to tumor progression.