Ellis et al. (2009) demonstrated the antitumor actions of low-dose estrogen therapy in postmenopausal women with advanced adjuvant aromatase inhibitor–resistant BC (deprivation ≥2 years). Iwase et al. (2013), using ethinylestradiol in patients with MBC (median age 63 years), had a 56% clinical benefit rate. Chalasani et al. (2014), using E2 during 3-month exemestane breaks in patients with MBC, had measurable clinical activity. These clinical studies reaffirm the earlier laboratory findings that estrogen treatment after LTED with TAM in vivo leads to BC regression (Yao et al., 2000). The gene discussed is CYP19A1; the disease is breast cancer.