Genomic instability in terms of numerical chromosomal aberrations (aneuploidy) and structural DNA rearrangements(deletions, gene amplifications, and translocations) is of central importance in the process of tumor progression.Defects in the cell cycle control play a critical role in the destabilization of the tumor cell genome.The defects in cell cycle checkpoints surveying DNA-damage and ensuring the correct order of DNA-replication, chromosome alignment, and chromosome segregation are of particular importance.Using a combination of high-resolution techniques, we could detect and validate a wide range of genomic rearrangements in samples from patients with breast cancer.Specific patterns of genomic copy number variations were found to be strongly correlated to clinical data,particularly the development of distant metastasis.In low-grade malignant tumors that rarely progress to metastatic diseases, few chromosomal rearrangements were seen.Aggressive tumors that readily develop distant metastases showed an increased number and specific patterns of regional chromosomal rearrangements.