ESR1 and breast cancer: Out of the informative cases, 94 patients (8%) had ER−/PR+ (ER < 1% and PR > 1%) breast cancers, while 676 (58.4%) had ER+/PR+ (ER > 1% and PR > 1%), 88 (7.6%) had ER+/PR− (ER > 1% and PR < 1%), and 164 (14.2%) had ER−/PR− (ER < 1% and <PR 1%) tumors.