Impact of CDK4/6 inhibitors on chemotherapy utilization in earlier therapy lines for HR+/HER2- metastatic breast cancer in the United States.

This population-based study illustrates that chemotherapy utilization in earlier therapy lines for HR+/HER2- MBC declined steadily between 2010 and 2019. These declines were significantly accelerated by the introduction of CDK4/6 therapy class in 2015, notably in the second- and third-line settings.