Background: Chromosomal aberrations in breast tumors from BRCA1 and BRCA2 germ-line mutation carriers are considerably more frequent than what is seen in sporadic breast tumors. According to Comparative Genomic Hybridisation analysis (CGH), deletions on chromosome 4 are one of the most frequent events in BRCA1-associated tumors, suggesting inactivation of specific tumor suppressor genes.
Materials and methods: In the present study, 16 microsatellite markers covering chromosome 4 were used to map loss of heterozygosity (LOH) in tumors from BRCA1 (n=41) as well as in tumors from BRCA2 (n=66) mutation carriers and in tumors from unselected cases of breast cancer (n =68).
Results: The frequency of LOH in these groups ranged from 16-73% in BRCA1-associated tumors, 13-42% in BRCA2-associated tumors and 8-33% in unselected tumors. LOH was significantly more frequent in BRCA1-associated tumors as compared to BRCA2-associated tumors and unselected tumors, and particularly high (over 70%) at 4q35.2. Pathological variables that were found significantly associated (p< or =0.05) with LOH at specific markers were: high percentage of cells in S-phase, negative estrogen receptor status, young age at diagnosis and large tumors. Deletion mapping indicates the existence of seven non-overlapping regions at chromosome 4, which were identified in all three groups of tumors. Three of these seven regions, 4p16.3-p16.1, 4q27-q32.1 and 4q35.1-4qter, have not been reported in breast cancer previously.
Conclusion: The results manifest the frequent alterations of chromosome 4 in BRCA1-associated breast tumors and indicate the location of several genes of potential importance in breast cancer development.