Clinical benefit and safety profile of cross-line therapy with CDK4/6 inhibitors: a retrospective study of HR+/HER2– advanced breast cancer

CDK4/6 inhibitors (CDK4/6is) in combination with endocrine therapy have secured a central role in the treatment of hormone receptor (HR)-positive advanced breast cancer (ABC) and have transformed the therapeutic landscape. Cross-line CDK4/6i therapy in which another CDK4/6i is continued after progression on a prior CDK4/6i may still offer advantageous therapeutic effects. Cross-line CDK4/6i therapy is an area of active investigation in the ongoing pursuit to improve outcomes for patients with HR+/human epidermal growth factor receptor 2 (HER2)- ABC.