Overall survival associated with CDK4/6 inhibitors in patients with HR+/HER2– metastatic breast cancer in the United States: A SEER‐Medicare population‐based study.

Background: Evidence on overall survival (OS) with cyclin‐dependent kinase 4 and 6 (CDK4/6) inhibitors is generally limited to data from clinical trials or a few observational studies with limited generalizability to Medicare population. The aim of this study was to determine OS benefits associated with CDK4/6 inhibitors in older Medicare patients with hormone receptor (HR)–positive and human epidermal growth factor receptor‐2 overexpressing (HER2–) metastatic breast cancer (MBC). Methods: In a retrospective cohort design, female patients aged ≥65 years with diagnosis of HR+/HER2– MBC from 2015 to 2017 who initiated first‐line systemic therapy within 12 months of MBC diagnosis were selected from the Survey Epidemiology and End Results‐Medicare database. The effect of treatment type (endocrine therapy [ET]+CDK4/6 inhibitor vs. ET alone) on OS was analyzed using Kaplan–Meier methods and multivariable Cox regression models. Adjusted hazard ratio (aHR) and 95% CIs were estimated. Results: A total of 630 eligible patients were identified (169 patients treated with ET+CDK4/6 inhibitor and 461 patients treated with ET alone). In the Kaplan–Meier analysis, OS rate at 3 years after first‐line treatment initiation was 73.0% for ET+CDK4/6 inhibitor versus 49.1% for ET alone (log‐rank p <.0001). In Cox regression analysis, first‐line ET+CDK4/6 inhibitor therapy was associated with 41% lower rate of mortality versus ET alone (aHR, 0.590; 95% CI, 0.423–0.823). Conclusions: The findings of this real‐world study demonstrate significant OS benefit associated with ET+CDK4/6 inhibitor therapy over ET alone in an older Medicare population of patients with HR+/HER2– MBC, largely consistent with the evidence from clinical trials. In patients with metastatic breast cancer (MBC) receiving treatment with cyclin‐dependent kinase 4 and 6 (CDK4/6) inhibitors, evidence on overall survival is generally limited to data from clinical trials or observational studies not generalizable to patients in the Medicare population. The findings of this real‐world analysis demonstrate that the addition of CDK4/6 inhibitors to endocrine therapy (ET) significantly improved survival among older Medicare beneficiaries, suggesting that treatment with ET alone should have a limited role in early lines of therapy for Medicare patients with HR+/HER2– MBC. [ABSTRACT FROM AUTHOR]