Chromosome 8 Losses in Colorectal Carcinoma: Localization and Correlation With Invasive Disease

Background: Allelic losses from the short arm of chromosome 8 (8p) are frequent in a variety of epithelial malignancies. In colorectal cancer, there are two discrete regions of 8p loss of hterozygosity (LOH), suggesting the existence of two putative tumor suppressor genes. Previous studies have shown an association of 8p LOH with tumor invasiveness. To better define the deletion extent and the clinical significance of these losses, a series of 41 colorectal cancers were examined for 8p LOH and correlated with clinical features. Methods and Results: Paired normal and enriched tumor DNA from the same individual was typed by polymerase chain reaction for 11 microsatellite polymorphisms and scored as positive or negative for 8p LOH. Loss of 8p markers was observed in 44% of the cases. Most cases had large deletions, but several had localized interstitial losses, enabling specification of two nonoverlapping regions of LOH. The telomeric region of loss is defined by the markers D8S262 and D8S133 at 8p22, and the centromeric region is proximal to NEFL. Clinical, histopathologic, and molecular data were obtained and a significant correlation of 8p LOH with microinvasion (invasion of lymphatics, vessels, or perineurium, ascertained by light microscopy) (P=.01) and also with loss of chromosome arm 18q (P=.001) was found. Conclusions: An association of 8p allelic loss with poor outcome was demonstrated. The correlation between 8p loss and 18q loss suggests that 8p LOH is a late event in the multistep model of colorectal carcinogenesis. 8p LOH may provide a clinically useful prognostic marker in colorectal cancer, thereby warranting further testing. The involvement of two independent loci on 8p is confirmed, and the refined localization of these sites will contribute to the eventual identification of these genes, which appear to play an important role in the progression of epithelial malignancies.