Antiestrogen resistance is a major clinical limitation in treatment of breast cancer. We have recently reported that Aurora A and Mcl-1 (myeloid cell leukemia 1) are potential novel treatment targets in antiestrogen-resistant breast cancer cells and that Aurora A expression is a biomarker for tamoxifen resistance in breast cancer patients. Abbreviations: Bcl-2, B-cell lymphoma 2; EGF, epidermal growth factor; ERα, estrogen receptor α; Mcl-1, myeloid cell leukemia 1; VEGF, vascular endothelial growth factor.