This was followed by the novel discovery that this Aurora B kinase inhibitor downregulated Aurora B protein level by increasing polyubiquitination and proteasomal degradation of Aurora B. Together, these studies indicate that AZD1152 has antineoplastic activity in human breast cancer cells and that AZD1152's impact on Aurora B protein stability is another important layer of regulation that has not been characterized before. This evidence concerns the gene AURKB and breast cancer.