ESR1 and breast cancer: Among the group categorized as hormonal receptor negative breast cancer (majority ER− breast cancers), we found increased risk for TNBC (ER−, PR−, HER2−), a finding consistent with a few studies that previously examined the TNBC subtype (Dolle et al. 2009; Trivers et al. 2009), although one prior study did not find this effect (Kabat et al. 2011), but did not find increased risk for HER2− overexpressing breast cancer (ER−, PR−, HER2+).