Genetic alterations and rearrangements occur frequently in cancer and contribute to its pathogenesis. Detecting these aberrations by array CGH provides information on the locations of important cancer genes and can have clinical use in diagnosis, cancer classification and prognostification. However, not all of the losses of genetic material are pathogenetic, since some DNA material is physiologically lost during the rearrangement of immunoglobulin subgenes. In a recent study, array CGH has been implemented to identify regions of chromosomal aberration (copy-number variation) in several mouse models of breast cancer, leading to identification of cooperating genes during myc-induced oncogenesis.