Efficacy and Safety of CDK4/6 Inhibitor Therapy in Patients Aged 70 and Older with Metastatic Breast Cancer: A Retrospective Single-Center Analysis

Objective: This study aimed to evaluate the effectiveness and safety of CDK4/6 inhibitor therapy in patients aged 70 years diagnosed with hormone receptor-positive (HR+) HER2-negative metastatic breast cancer (MBC).Given the unique challenges faced by older adults due to comorbidities and potential treatment-related toxicities, this study aimed to provide insights into real-world outcomes in this population.Methods: This retrospective, single-center analysis included 43 patients aged 70 years diagnosed with HR+ HER2-MBC who started CDK4/6 inhibitor treatment between May 2020 and December 2022.Data were collected from medical records, including demographics, ECOG performance status, treatment details, and adverse events.Progression-free survival (PFS) and overall survival (OS) were evaluated using Kaplan-Meier analysis, whereas subgroup comparisons were performed using log-rank tests.Cox proportional hazard models were used to identify the factors associated with PFS and OS. Results:The median age was 76.7 years, and 46.5% of the patients presented with de novo metastasis.CDK4/6 inhibitors were administered as first-line treatment in 41.9% of patients, second-line therapy in 46.5 %, and third-line therapy in 11.6 %.The median PFS was 16.0 months, with patients with ECOG PS 0 or 1 achieving significantly longer PFS (20.0 months) than those with ECOG PS2 (5.8 months, p<0.01).The median OS was 25.3 months, with better outcomes for ECOG PS 0 or 1 (29.3 months) than for ECOG PS2 (15.9 months, p<0.01).Dose reductions occurred in 32.6% of patients but did not significantly affect the PFS. Conclusion:CDK4/6 inhibitors are effective in older adults with HR+ HER2-MBC, particularly those with an ECOG PS of 0 or 1 with manageable toxicities with dose reductions.These findings highlight the importance of assessing ECOG PS when managing treatment in older patients.Dose adjustments were feasible without compromising efficacy, suggesting that personalized treatment can optimize outcomes.Further research with larger cohorts is required to confirm this hypothesis.