Analysis of genomic DNA copy number alterations in chromosome arm 18q demonstrates distinct molecular categories of colorectal carcinoma

Abstract

10005 Background: Genomic instability is a major feature of neoplastic development in colorectal carcinoma and other cancers. Specific genomic instability events such as genomic deletions have potential utility as biologically relevant prognostic biomarkers. Loss of heterozygosity (LOH) on chromosome arm 18q is an indicator of colorectal carcinoma behavior and potentially, prognosis. For stage II and III colorectal cancer, a number of retrospective studies have shown strong correlations between deletions in 18q and reduced survival. However, other studies have failed to identify this correlation. This discrepancy is likely the result of different sets of genetic markers and their widely disparate locations along chromosome arm 18q, often separated by megabases. New technologies are needed to overcome these issues. Methods: Using a novel genomic technology called molecular inversion probes (MIPs), we analyzed genomic deletions at exon-level resolution in primary colorectal carcinoma. Unlike microsatellite genetic markers, MIPs are not dependent on having informative alleles to discern a LOH event. This enables querying microsatellite genetic markers used in any clinical study. We designed a set of probes to interrogate several hundred individual exons of over two hundred cancer genes with an overall distribution covering all chromosome arms. Also represented were a series of over 100 probes along chromosome arm 18q representing genetic markers used in clinical studies. An analysis was carried out on primary tumor samples from patients with stage II and III disease. Results: We discovered several distinct categories of colorectal carcinomas based upon their profile of 18q genomic deletions and other allelic imbalances. Colorectal carcinoma extent of invasion showed an association with cluster designation which suggests that the multiple genomic instability events influence the invasive behavior of colorectal carcinoma. Conclusions: Colorectal cancer has distinct patterns of 18q genomic deletions, representing a potential molecular classifier. This finding has potential clinical ramifications given the application of 18q LOH events as an indicator for adjuvant treatment in stage II colorectal carcinoma. No significant financial relationships to disclose.