CDK4/6 inhibitor Ibrance is emerging as a combination partner for metastatic breast cancer drug developers based on its long-accumulated treatment experience. Even if the dose is increased, there is little concern about side effects, so it is expected that it will be used as a variety of combination drugs. Ibrance is the first CDK4/6 inhibitor developed by Pfizer and was launched in Korea in the fourth quarter of 2016. It provided a new treatment option for patients with HR+/HER2- metastatic breast cancer who had to use anti-hormonal drugs such as aromatase inhibitors or chemotherapy if not managed with these drugs. Ibrance, which held the top spot in the CDK4/6 market for five years, faced a decline for the first ti