In women with elevated risk of breast cancer, studies have shown that adjuvant endocrine therapy with a selective estrogen receptor modulator or an aromatase inhibitor reduces the risk by 40–50 % [38–40], and in women with lobular and ductal cancer in situ some studies suggest that the benefits are even greater [12, 38, 41, 42]. This evidence concerns the gene CYP19A1 and breast carcinoma.