ESR1 and breast cancer: In 2015, Bae et al8 reported that ER-positive/PR-negative and ER-negative/PR-positive tumors are associated with poorer disease-free survival and OS than ER-positive/PR-positive tumors, but they found that ER-positive/PR-negative and ER-negative/PR-positive tumors are associated with poor survival similar to that of the ER-negative/PR-negative subtype in ERBB2-negative BC; there was no difference in survival among the 4 subtypes in patients with ERBB2-positive disease.