ESR1 and breast cancer: Table 2 summarizes the clinical and pathological features of 574 early-stage breast cancer patients treated initially by conservative surgery and sentinel node procedure, between 2005 and 2011 at Institut Curie, Saint-Cloud. 480 (84%) tumours were classified as ER positive HER2 negative, 45 (8%) were ER negative HER2 negative, 32 (6%) were ER positive HER2 positive and 17 (3%) were ER negative HER2 positive.