ESR1 and breast cancer: PTEN loss is ranked as ESCAT Tier IIA and 23 breast cancers were mutated in PTEN. There were 2 ER+/HER2+, 14 ER+/HER2-, 2 ER−/HER2+, and 5 ER−/HER2- cases among 8, 1, 5, 2, and 7 Group 1A, 1B, 2, 3–1, retrospective cohort groups.