Cyclin Inhibitors in Advanced Breast Cancer: Evaluation of Toxicity in Older Patients

Cyclin-dependent kinase (CDK) 4/6 inhibitors have improved survival outcomes in advanced breast cancer. Real-world data on tolerability and effectiveness in older patients are still scarce. This retrospective study analyzed data from patients with advanced hormone receptor-positive and HER2-negative breast cancer receiving CDK4/6 inhibitors as first-line treatment from July 2017 to June 2024. The aim was to evaluate the toxicity and effectiveness of that therapy in older (≥ 65 years) patients. A total of 79 female patients were included, with a median age of 62 years, 39.2% were ≥ 65 years. Patients aged ≥ 75 years constituted 19.0% of the total sample. No statistically significant difference in toxicity rates was observed between patients aged ≥ 65 and < 65 (p = 0.078), but toxicity was significantly higher in patients ≥ 75 years compared to the remaining patients (p = 0.030). The incidence of grade ≥ 3 toxicity did not differ significantly between age groups. One-year progression-free survival was 71.0% in patients ≥ 65 and 64.6% in patients < 65 (p = 0.555), with a hazard ratio for progression/death of 0.63 (95% CI: 0.33 - 1.21, p = 0.168). Although there was a higher rate of overall toxicity among older patients, CDK4/6 inhibitors were well tolerated in this sample.