For many years, it was assumed that gene fusions were a type of mutation confined largely to leukemias and sarcomas. However, fusion genes are now known to be important in several epithelial cancers and a number have been described in breast cancers. In the December 2011 issue of Nature Medicine, Robinson and colleagues reported many more gene fusions -including the first recurrent fusion, SEC16A-NOTCH1 - in breast cancers. Several genes, including members of the MAST (microtubule-associated serine threonine) kinase and Notch gene families, are fused more than once. This finding supports an emerging story that most breast cancers express a number of fusion genes.