ESR1 and breast cancer: For Australian women enrolled in the Melbourne Collaborative Cohort Study, compared to never use, recent MHT use (current or last use in the past year) was associated with a significantly increased risk for ER+ but not ER- breast cancers (when examined by ER status alone), for PR+ but not PR- breast cancers (when examined by PR status alone) and for both ER+/PR+ and ER-/PR-breast cancers, although there was no statistical heterogeneity in the hazard ratios across subtypes defined by ER, PR or ER/PR status (n = 336 breast cancers in a cohort of 13,444 women) [36].