Ahern and colleagues also studied the Unites States registered nurses database, where the results indicated higher HR in digoxin users in the estrogen receptor (ER)-positive breast cancer (HR = 1.45; 95% CI: 1.13–1.86) compared to the ER-negative breast cancer (HR = 1.21; 95% CI: 0.52–2.37) (Ahern et al., 2014). This evidence concerns the gene ESR1 and breast carcinoma.