Chromosomal rearrangements and oncogene amplification precede aneuploidization in the genetic evolution of breast cancer

Breast carcinoma is thought to arise because of multiple successive changes in the genome of the normal epithelial cells. However, little is known of the order of appearance of different types of genetic aberrations. We studi ed the ERBB2 (Her-2/neu) and CCND1 (cyclin D1) oncogene amplification in fl ow cytometrically sorted diploid and nondiploid tumor cell populations by f luorescence in situ hybridization (FISH), The purity of the fell sorting wa s confirmed by static DNA image cytometry, Spectral karyotyping was used to define differences in a genome-wide manner between two distinctly differen t aneuploid cell clones found in each of two breast cancer cell lines. FISH indicated the presence of gene amplification both in diploid and nondiploi d cell clones in 17 of the 21 amplification-containing tumors analyzed. The oncogene copy numbers remained unchanged throughout aneuploidization in 11 of 17 tumors, The remaining six tumors showed an increase in oncogene copy number as well as the number of chromosome 11 or 17 centromeres (the origi nal location of CCND1 and ERBB2, respectively), Breast carcinoma cell lines MDA-157 and MDA-436 showed a significant number of chromosomal rearrangeme nts in the near-diploid clones, which were present in duplicate in the corr esponding aneuploid (polyploid) clones. These results indicate that ploidy shin, i.e., aneuploidization, in breast cancer is a late genetic event, whi ch is preceded by both oncogene amplifications as well as many chromosomal rearrangements.