As breast cancer is the second most common cancer in women and approximately 40% of HR+/HER2- advanced breast cancer patients have a PIK3CA mutation, alpelisib will be prescribed more by oncologists and, therefore, appropriate screening with fasting plasma glucose, hemoglobin A1c (HbA1C), and monitoring during drug administration is of utmost importance. The gene discussed is PIK3CA; the disease is breast cancer.