ESR1 and breast cancer: We evaluated the prognostic and predictive value of HSD17B1 and HSD17B2 expression in breast tumors.<h4>Methods</h4>We identified a cohort of premenopausal breast cancer patients from the Danish Breast Cancer Group database (2002-2011) and stratified on ER status and receipt of tamoxifen (4600 ER+/TAM + and 1359 ER-/TAM-).