Background: Previous studies demonstrated the tolerability of palbociclib plus endocrine therapy (ET). This analysis evaluated safety based on more recent cutoff dates and a longer palbociclib treatment exposure.
Patients and methods: Data were pooled from three randomized studies of patients with hormone receptor-positive/human epidermal growth factor receptor 2-negative (HR+/HER2-) advanced breast cancer (ABC), including postmenopausal women who had not received prior systemic treatment for advanced disease (PALOMA-1/-2) and pre- and postmenopausal women who had progressed on prior ET (PALOMA-3).
Results: Updated cutoff dates were December 21, 2017 (PALOMA-1), May 31, 2017 (PALOMA-2), and April 13, 2018 (PALOMA-3). Total person-years of treatment exposure were 1,421.6 with palbociclib plus ET (n = 872) and 528.4 with ET (n = 471). Any-grade neutropenia and infections were more frequent with palbociclib plus ET (82.1% and 59.2%, respectively) than with ET (5.1% and 39.5%). The hazard ratios were 1.6 (p = .0995) for grade 3/4 infections, 1.8 (p = .4358) for grade 3/4 viral infections, 1.4 (p = .0001) for infections, and 30.8 (p < .0001) for neutropenia. Febrile neutropenia was reported in 1.4% of patients receiving palbociclib plus ET. Cumulative incidence of all-grade hematologic adverse events in both arms peaked during the first year of treatment and plateaued over the 5 subsequent years. Interstitial lung disease was reported in 13 patients receiving palbociclib plus ET and 3 receiving ET.
Conclusion: This 5-year, long-term analysis demonstrated that palbociclib plus ET has a consistent and stable safety profile and is a safe treatment for patients with HR+/HER2- ABC.
Implications for practice: Several treatments for patients with breast cancer are associated with long-term or latent adverse events. This long-term, 5-year analysis demonstrated that palbociclib plus endocrine therapy has a consistent and stable safety profile without cumulative or delayed toxicities. These results further support palbociclib plus endocrine therapy as a safe and manageable treatment in clinical practice for patients with hormone receptor-positive/human epidermal growth factor receptor 2-negative advanced breast cancer.
Keywords: Advanced breast cancer; HR+/HER2−; Long-term safety; Palbociclib; Pooled safety.
© 2021 The Authors. The Oncologist published by Wiley Periodicals LLC on behalf of AlphaMed Press.