ESR1 and breast cancer: In a retrospective study of 131 patients who received SRS for breast cancer brain metastases between 2001 and 2013 revealed a median overall survival of 16, 26, 23, and 7 months for ER positive/HER2 negative, ER positive/HER2 positive, ER negative/HER2 positive, and TNBC (triple negative breast cancer), respectively (p < 0.001) (32).