Tolerability and effectiveness of palbociclib in older women with metastatic breast cancer.

Purpose: Palbociclib has become the standard of care for estrogen receptor-positive (ER+), human epidermal growth factor receptor 2 negative (HER2-) metastatic breast cancer, but real-world evidence in older women remains scarce. Therefore, we investigated tolerability of palbociclib in older women with metastatic breast cancer.

Methods: Consecutive women aged ≥ 70 with ER+/HER2- metastatic breast cancer, treated with palbociclib in any treatment line in six hospitals, were included. Primary endpoint was grade ≥ 3 palbociclib-related toxicity. Predictors of toxicity were identified using logistic regression models. Progression-free survival (PFS) and overall survival (OS) were estimated using Kaplan Meier.

Results: We included 144 women with a median age of 74 years. Grade 3-4 toxicity occurred in 54% of patients, of which neutropenia (37%) was most common. No neutropenic fever or grade 5 toxicity occurred. Dose reduction during treatment occurred in 50% of patients, 8% discontinued treatment due to toxicity and 3% were hospitalized due to toxicity. Polypharmacy (odds ratio (OR) 2.50; 95% confidence interval (CI) 1.12-5.58) and pretreatment low leukocytes (OR 4.81; 95% CI 1.27-18.21) were associated with grade 3-4 toxicity, while comorbidities were not. In first-line systemic therapy, median PFS was 12 months and median OS 32 months. In second-line, median PFS was 12 months and median OS 31 months.

Conclusion: Although grade 3-4 toxicity and dose reductions occurred frequently, most were expected and managed by dose reductions, showing that palbociclib is generally well tolerated and thus represents a valuable treatment option in the older population.