ESR1 and breast cancer: Clinically, most patients had stage T2 tumors (67%, n = 764) and node-positive BC (56%, n = 644); 44% of tumors were luminal (n = 508), 31% were TNBC (n = 359) and 24% were HER2-positive BC (n = 281), including 134 HER2+/ER− and 147 HER2+/ER+.