ESR1 and breast cancer: We characterize the ribonucleic acid (RNA) expression of phosphatases in estrogen receptor-positive (ER+), estrogen receptor-negative (ER−) BC and in the two major subgroups of ER− BC [epidermal growth factor receptor 2-positive (ERBB2+) and epidermal growth factor receptor 2-negative (ERBB2−)] by expression microarrays.