• Akaolisa Samuel Eziokwu, Leticia Varella, Megan Lynn Kruse, Xuefei Jia, MooreHalle C FHCFTaussig Cancer Institute, Cleveland Clinic, Cleveland, OH., Thomas BuddGeorgeGTaussig Cancer Institute, Cleveland Clinic, Cleveland, OH., Jame Abraham, and Alberto J Montero.
• Taussig Cancer Institute, Cleveland Clinic, Cleveland, OH. Electronic address: akalisaz@gmail.com.
• Clin. Breast Cancer. 2021 Jun 1; 21 (3): 205-209.

BackgroundCDK4/6 inhibitors (CDK4/6i), in combination with aromatase inhibitors, are United States Food and Drug Administration-approved for the treatment of hormone receptor-positive (HR+)/human epidermal growth factor receptor 2-negative (HER2-) metastatic breast cancer (MBC). The effectiveness of continuing them beyond first disease progression (PD) is currently unknown. This retrospective study evaluated the impact of the continuation of CDK4/6i beyond first PD in HR+/HER2- MBC using real-world experience.Patients And MethodsA single-institution retrospective review of patients with HR+ MBC who received CDK4/6is from 2015 to 2018 and where CDK4/6is were continued beyond first PD. The primary outcome was progression-free survival (PFS) after initial PD on CDK4/6i therapy.ResultsThirty women with HR+/HER2- MBC met eligibility criteria. Patients were identified from a prospective database of patients at the Cleveland Clinic Foundation who were prescribed CDK4/6is. The median age and follow-up duration were 47.5 years and 27 months, respectively. Most patients received palbociclib (PA)/letrozole as initial therapy (67%), followed by PA/fulvestrant (23%), and PA/other aromatase inhibitor (20%), and abemaciclib with either fulvestrant or letrozole (6%). As of January 31, 2019, 25 (83.3%) patients were still alive, and 19 (63%) patients had progressed. The estimated median PFS for continued CDK4/6i use beyond the first PD was 11.8 months (95% confidence interval, 5.34-13.13 months).ConclusionsAmong a small cohort of patients with HR+ MBC in a non-clinical trial setting, continuation of CDK4/6i-endocrine treatment post initial PD was associated with a median PFS of about 12 months. Formal randomized clinical trials evaluating the continuation of CDK4/6is beyond the first PD are currently ongoing and will provide more answers to this important clinical question.Copyright © 2020 Elsevier Inc. All rights reserved.

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