ESR1 and breast cancer: The method presented in Wang et al was applied to the MDA133 breast cancer microarray dataset previously published by Hess et al.1,7 The MDA133 microarray dataset is accompanied by clinical information including immunohistochemistry (IHC) scores for markers currently used to evaluate breast cancer, including estrogen receptor (ESR1), progesterone receptor (PGR), and human epidermal growth factor receptor 2 (HER2, or ERBB2).