PURPOSE: The aim was to understand real-world cyclin-dependent kinase (CDK) 4 and 6 inhibitor use in Japan. METHODS: This retrospective observational study used a Japanese administrative claims database and included patients with presumptive hormone receptor-positive, human epidermal growth factor receptor 2-negative advanced breast cancer (ABC) prescribed CDK4 and 6 inhibitor therapy between December 2017 and March 2021. Patient characteristics, treatment patterns, and selected clinical and safety outcomes were descriptively summarized. Time to discontinuation (TTD) and chemotherapy-free survival (CFS) were examined using Kaplan-Meier estimates. RESULTS: The study cohort (N = 6442) was predominantly female (99.4%; median [range] age 64 [26-99] years) with records of metastases (79.6%) within 1 year prior to initiating CDK4 and 6 inhibitor therapy. In total, 4463 (69.3%) and 1979 (30.7%) were prescribed palbociclib and abemaciclib, respectively, as their first CDK4 and 6 inhibitor, most commonly in combination with fulvestrant (n = 3801; 59.0%). Overall, 3756 patients initiated a subsequent anticancer treatment, of whom 748 (19.9%) initiated a different CDK4 and 6 inhibitor in combination with the same or different endocrine therapy. Median TTD (95% confidence interval) was 9.7 (9.3, 10.1) months for the first CDK4 and 6 inhibitor therapy. Median CFS was 26.1 (24.6, 27.8) months. Incidence of clinically relevant diarrhea was higher after abemaciclib initiation (9.8%) than after palbociclib initiation (1.5%). More patients experienced dose reduction with palbociclib (69.3%) than with abemaciclib (53.0%). CONCLUSION: The data provide insights into current clinical practices for CDK4 and 6 inhibitor use in Japan that could help establish future treatment strategies for ABC.
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Kawai et al. (2022) studied this question.
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