Amplification of chromosomal regions leads to an increase of DNA copy number and expression of oncogenes in human breast cancer (HBC). Amplification of the 8p11-p12 region occurs in 10-15% of primary, uncultured HBCs. In our panel of 11 breast cancer cells, three cell lines, SUM-44, SUM-52, and SUM-225, have overlapping amplicons in the 8p11-p12 region. To characterize genome structure of the amplified regions, we performed fluorescence in situ hybridization using 8p11-p12 BAC clones in the 3 cell lines. The results revealed that the 8p11-p12 amplicon has a highly complex structure and that FGFR1 is not in the common core-amplified domain in 3 breast cancer cell lines with the amplicon. These 3 cell lines provide good models for genetic and functional studies of candidate oncogenes of the 8p11-p12 region.