ESR1 and breast cancer: Moreover, as to breast cancer subtypes, similar results were reported by Rakha et al., in 2007, who found that patients with estrogen receptor (ER)-negative/progesterone reception (PR)-positive and ER-positive/PR-negative tumors are distinct breast cancer phenotypes; they have more advanced clinicopathological features when compared with the double-positive and favorable feature when compared with double-negative breast cancers.