High incidence of loss of heterozygosity in breast tumors from carriers of the BRCA2 999del5 mutation.

Germ-line mutation in the BRCA2 gene confers an increased risk of breast cancer. An elevation of additional genetic defects in tumors of patients with germ-line mutation in the BRCA2 gene compared with sporadic breast tumors has been reported. To evaluate the nature of the difference, we did detailed mapping of chromosomes 1p, 3p, 6q, 11, 13q, 16q, 17, and 20q, using microsatellite markers. We found that the frequency of loss of heterozygosity was similar at some chromosomal regions in the BRCA2 999del5 and sporadic tumors but significantly different at others. These others include chromosomal arms 3p, 6q, 11p, 11q, 13q, and 17p. Loss of heterozygosity mapping suggests that the same chromosome regions are involved in both tumor groups but at elevated frequencies in BRCA2 999del5 tumors. This higher frequency of genetic aberrations could pinpoint genes that selectively promote tumor progression in individuals predisposed to breast cancer due to the BRCA2 999del5 germ-line mutation. Accumulation of somatic genetic changes during tumor progression may follow a specific and more aggressive pathway of chromosome damage in these individuals.