Breast cancer survivors treated with aromatase inhibitors alone and combined chemotherapy plus aromatase inhibitors had a greater than two- and threefold increased risk of osteopenia and osteoporosis compared with cancer-free women (MV-HR = 2.72, 95% CI = 1.31–5.65; MV-HR = 3.83, 95% CI = 1.87–7.83, respectively). The gene discussed is CYP19A1; the disease is osteoporosis.