ESR1 and breast cancer: Regarding the HR-specific subtypes, a profound heterogeneity was demonstrated in the prognosis of HER2-positive breast cancer patients with ER + /PgR + , ER + /PgR−, ER−/PgR + , ER−/PgR− subtypes, in which a successively worsening tendency existed in the survival with the 3-year OS rate of 91.8% (95% CI 91.6–92.0%), 87.8% (95% CI 87.4–88.2%), 84.7% (95% CI 83.4–86.0%), 85.9% (95% CI 85.6–86.2%) and 5-year OS rate of 85.8% (95% CI 85.5–86.1%), 80.5% (95% CI 79.9–81.1%), 79.4% (95% CI 77.7–81.1%), 78.8% (95% CI 78.3–79.3%) (P < 0.0001).