CanGEM

Genomic instability can be divided into 2 categories: chromosomal instability (CIN) and microsatellite instability (MSI). CIN has been linked to aneuploidy and chromosomal aberrations, and high-level loss of heterozygosity (LOH-H) has been suggested to be an indicator of CIN. High-level MSI (MSI-H), which results from nonfunctional mismatch repair, has previously been suggested to be mutually exclusive with CIN. Four MSI-H and three LOH-H primary gastric tumors of intestinal histology were used for copy number analysis by array-based comparative genomic hybridization (aCGH) with 13,000 cDNA targets. The MSI-H group showed fewer gains (0-12, average 4.5) and losses (0-10, average 2.5) per tumor as compared to the LOH-H group (9-15 gains, average 11.6 and 1-6 losses, average 4). Two MSI-H tumors did not show any copy number changes and one showed only gains of whole chromosomes. The most common alterations were gains of 20q (5/7 samples), 1q, 8, and 10p (3/7 samples) and losses of 1p and 5p (3/7 samples). The minimal amplified regions in 1q and 20q were localized to 1q21.1 approximately q21.2, 1q21.3, 20q11.2, 20q13.12, and 20q13.3 approximately qter. No copy number change was found to be specific for MSI-H or LOH-H. The results suggest that the LOH-H phenotype revealed by microsatellite analysis predicts reliably copy number abnormalities on aCGH and that a subset of MSI-H and all LOH-H tumors share the CIN phenotype.