[The Efficacy of CDK4/6 Inhibitors as Late Therapy in Patients Treated with Palbociclib and Abemaciclib Two Sequentially].

The combination of endocrine therapy and cyclin-dependent kinase 4/6 inhibitor(CDK4/6 inhibitor)is recommended as primary treatment for hormone receptor-positive HER2-negative metastatic or recurrent breast cancer. In this study, we investigated the efficacy and adverse events of CDK4/6 inhibitors as late therapy in patients treated with palbociclib(PLB) and abemaciclib(ABM)2 sequentially. Nine patients were selected with a history of prescriptions for 2 PLB and ABM drugs from December 2017 to November 2024. Efficacy and adverse events were examined retrospectively from the database. As a result, all patients were female, with an average age of 56 years old. There were 8 recurrent cases and 1 case of de novo Stage Ⅳ. Seven cases were changed to ABM after PLB, and 2 cases were changed from ABM to PLB. Median progression- free survival(PFS)as the late therapy for ABM was 29.2 months vs 6.5 months for PLB. One PD and 6 adverse events were the reasons for switching to ABM after taking PLB. Although the number of patients was small, PFS with sequential CDK4/6 inhibitors could be expected to be longer than 6 months, suggesting that the treatment may be useful in extending the time to chemotherapy induction.