ESR1 and breast cancer: In a retrospective study of 9639 patients with early BC, it was reported that (a) no significant difference was observed in recurrences between patients with ER-low and ER-negative tumors (19.4%) (p = 0.5), (b) for patients receiving ET, recurrence rates were higher in patients whose tumors were ER-low-positive compared with those that were ER-positive with ER expression ≥ 10% (17.7% versus 7.7%, p = 0.02) and (c) there was no significant difference in total recurrences between the groups of patients who did not receive ET [39].