In advanced breast cancer, high and moderate-quality evidence indicated that CDK4/6 inhibitors significantly increased AEs across all grades, including grade 3/4 AEs, leucopenia, grade 3/4 leucopenia, neutropenia, grade 3/4 neutropenia, anemia, grade 3/4 anemia, nausea, grade 3/4 constipation, fatigue, pyrexia, venous thromboembolism abdominal pain, and cough. The gene discussed is CDK4; the disease is neutropenia.