Genetic profiling of colorectal cancer liver metastases by combined comparative genomic hybridization and G-banding analysis

The majority of genetic studies of colorectal carcinogenesis have focused on changes found in primary tumors. Despite the fact that liver metastases are a leading cause of colorectal cancer deaths, the molecular genetic basis of the advanced disease stages remains poorly understood. We performed comparative genomic hybridization (CGH) on 17 liver metastases from colorectal carcinomas and compared the quantitative profile with the qualitative profile previously obtained with chromosome banding. An average of 12.6 aberrations per tumor was found by CGH. Chromosome 18 and chromosome arms 4q, 8p, and 17p were most frequently lost, whereas chromosomes 7 and 20 and chromosome arms 6p, 8q, and 13q were most frequently gained. We compared the chromosome banding and CGH data after converting the karyotypes into net copy number gains and losses. Ten tumors showed agreement between the findings of the two techniques, whereas five tumors did not (in two cases, no mitotic cells were obtained for banding analysis). All five discordant cases had a "simple" abnormal or normal karyotype, but revealed multiple changes by CGH. A likely explanation for this discrepancy is that in vitro growth before G-banding selected against the cancer cells. Interestingly, by comparing the CGH profiles of the "complex" vs. the "simple"/normal karyotype groups, deletion of 8p and gain of 16q were seen more frequently in the former group. The liver metastases had the same aberrations as seen in primary colorectal carcinomas, summarized in a literature survey. However, these aberrations were seen more frequently in liver metastases, which may be attributable to increased genetic instability. (C) 2003 Wiley-Liss, Inc.