MYB oncogene amplification in hereditary BRCA1 breast cancer

Comparative genomic hybridization analysis has demonstrated that breast tum ors from BRCA1 and BRCA2 germ-line mutation carriers contain a large number of chromosomal copy number gains and losses. A high regional copy number g ain at 6q22-q24 was observed in one BRCA1 tumor, and fluorescence in situ h ybridization analysis indicated a strong amplification of the MYB oncogene (15 copies of MYB compared with 1 copy of chromosome 6 centromere). Fluores cence in situ hybridization analysis revealed amplification of MYB in 5 (29 %) of 17 BRCA1 breast tumors, whereas none of 8 BRCA2 tumors and 13 breast cancer cell lines, and only 2 of 100 sporadic breast tumors exhibited alter ed MYB copy numbers, Gene amplification resulted in mRNA overexpression as determined by Northern blot and cDNA microarray analysis, and protein overe xpression by immunohistochemical staining. We conclude that MYB amplificati on is infrequent in sporadic breast cancer but common in breast tumors from BRCA1 mutation carriers, suggesting a role of this cell cycle regulator an d transcription factor in the progression of some BRCA1 tumors. However, we cannot rule out the significance of other genes in the 6q22-q24 amplicon.