ESR1 and cancer: High expression of oncogenic miR-21 in cancer cells from ER+ and/or PR+ HER2– cases and in tumor-associated fibroblasts from ER–, PR–, HER2– cases was associated with a poorer clinical outcome [Mackenzie TA, Schwartz G, Calderone H, et al. Stromal Expression Of miR-21 Identifies High-Risk Group In Triple Negative Breast Cancer, Submitted].