Methods: This preliminary study evaluated the QoL of life and dietary intake in 185 women with breast cancer on two therapies, aromatase inhibitors (AIs) and tamoxifen, using the Functional Assessment of Cancer Therapy—Endocrine Symptoms (FACT-ES), European Organization for Research and Treatment of Cancer Quality of Life Questionnaire (EORTC QLQ-C30), and Breast Cancer Specific Questionnaire (QLQ-BR23) and a 24 h dietary recall. The gene discussed is CYP19A1; the disease is breast cancer.