In the context of breast cancer, an estrogen-dependent cancer, where the use of aromatase inhibitors has been highly researched [47–51], deleterious effects of non-specific delivery of Letrozole includes osteoporosis leading to increased bone fractures, joint and muscle pain, menopausal symptoms, depression, cardiac problems, increased cholesterol and increased blood pressure were shown. The gene discussed is CYP19A1; the disease is depressive disorder.