Hormone receptor-positive, recurrent, or stage IV breast cancer in postmenopausal women is often managed with endocrine therapies, such as the nonsteroidal aromatase inhibitor letrozole [1], whereas primary treatment options for patients with human epidermal growth factor receptor 2 (HER2)-negative locally recurrent or metastatic breast cancer include single-agent cytotoxic chemotherapeutic agents, such as paclitaxel [1, 2]. The gene discussed is CYP19A1; the disease is breast cancer.