Title: Effectiveness of Changing the Class of Molecularly Targeted Agent after Disease Progression during Initial Molecularly Targeted Therapy for Luminal Advanced/Metastatic Breast Cancer
Abstract: The emergence of molecularly targeted agents (MTAs) has altered the treatment landscape for hormone receptor-positive (HR+), human epidermal growth factor 2-negative (HER2-) advanced breast cancer (ABC) /metastatic breast cancer (MBC). Multiple guidelines recommend molecularly targeted therapy as first-line treatment for HR+/HER2- ABC/MBC. However, optimal treatment for disease progression during MTA therapy remains undetermined. This study evaluated the suitability of different MTA types for this patient subgroup.In this retrospective study, we analyzed the electronic health records of 56 patients with HR+/HER2- ABC/MBC receiving treatment with palbociclib, abemaciclib, or everolimus in our center between April 2014 and June 2021.Overall, 39, 14, and 35 regimens using palbociclib, abemaciclib, and everolimus, respectively, were identified. Three and 53 patients were premenopausal and postmenopausal, respectively. MTAs were included in the 1st-11th lines of treatment. Time to failure (TTF) was significantly different among the three MTAs. In contrast, TTF did not significantly differ among the 50 regimens that included CDK4/6 inhibitors, with/without prior mTOR inhibitor use, and the 35 regimens that included mTOR inhibitors, with/without prior CDK4/6 inhibitor use.The sequential use of different MTA classes did not affect the TTF of another MTA. mTOR inhibitor + exemestane is a favorable treatment option after CDK4/6 inhibitor + hormone therapy, and CDK4/6 inhibitor + hormone therapy is suitable for patients previously treated with mTOR inhibitor + exemestane. Although this study was retrospective and conducted at a single center, the present findings are useful for treatment selection in clinical practice.