Genome-wide search for loss of heterozygosity shows extensive genetic diversity of human breast carcinomas.

Deletions of genomic regions involving tumor suppressor genes are thought to be important in the initiation and progression of breast cancer. We conducted a genome-wide search for deleted regions in a series of 75 human breast carcinomas by studying the allelic patterns of 184 microsatellite markers distributed over all chromosomes and looking for loss of heterozygosity (LOH). We identified 56 regions of consistent LOH. Strikingly, every tumor had a different set of deletions. To study this complexity, we applied a phylogenetic-like type of analysis. Each region was involved in a certain proportion of tumors, ranging from 20 to 62%; the most frequently involved regions were on chromosome arms 8p, 11q, 16q, and 17p. There was a correlation (P = 0.005) between the level of LOH and the size of the tumors. Tumors with a high level of LOH were also highly proliferative and had a high mitotic index.