When considering ER together with PR status, we found strongest associations of ever smoking with ER+/PR- breast cancer (1.75; 1.12–2.71), weaker with ER+/PR+ breast cancer (1.27; 1.02–1.59), and none with ER−/PR- (1.08; 0.72–1.611) or ER−/PR- (1.02; 0.26–4.07) breast cancer (Table 5). The gene discussed is ESR1; the disease is breast cancer.