Age, Age‐Related Comorbidities and Survival in Palbociclib, Ribociclib and Abemaciclib Users With Advanced Breast Cancer: A Nation‐Wide Retrospective Cohort Study

PURPOSE: Prevalence of breast cancer (BC) increases with age, but the external validity of data obtained from pivotal trials of medicinal products remains a concern due to the underrepresentation of frail and older adults. Cyclin-dependent kinase inhibitors (CDKi), palbociclib, abemaciclib, and ribociclib are considered an essential part of the standard-of-care in the management of advanced/metastatic breast cancer. We investigated age, comorbidities, and survival in a nationwide real-world cohort of CDKi users. METHODS: Data from the Finnish Cancer Registry, reimbursed dispensed prescriptions, Electronic Prescription Database, Care Register for Health Care (CRHC), and Causes of Death Register were combined and analysed. RESULTS: Altogether 1921 women with BC initiated CDKi treatment in 2018-2022. The median age at initiation was 66.9 years, with 43.2% of the study cohort being < 65 years of age, 36.1% 65-74 years, 19.0% 75-84 years, and 1.7% 85 years or older. The prevalence of age or frailty-related comorbidities in individuals ≥ 65 years was low, highest for cardiovascular diseases, 32.3%, and diabetes, 16.9%. The median survival was 25.3 months, with longer median survival times in younger age groups (27.7 months in < 65 year-olds, 25.1 months in aged 65-74, 21.4 months in aged 75-84 years, and 15.4 months in 85 years or older). CONCLUSIONS: Real-world CDKi users are older than women included in the pivotal trials, and the survival differences between age groups imply challenges in the generalisability of data from pivotal trials. The real-world CDKi user population is characterised by a low prevalence of major comorbidities.