INTRODUCTION: Cyclin-dependent kinase 4/6 inhibitors (CDK4/6is) in combination with endocrine therapy are the current standard of care for first line (1L) treatment of hormone receptor–positive and human epidermal growth factor receptor 2–negative (HR+/HER2–) metastatic breast cancer (mBC). To investigate the effectiveness of palbociclib, the first-in-class CDK4/6i, plus an aromatase inhibitor (AI) in older patients, we compared overall survival (OS) in a Medicare population treated with 1L palbociclib+AI versus an AI alone.
METHODS: Patients aged ≥65 years who were diagnosed with de novo HR+/HER2– mBC from 2015–2019 were identified from the Surveillance, Epidemiology, and End Results (SEER)–linked Medicare database and were eligible if they initiated 1L palbociclib+AI or an AI alone. The primary endpoint was OS. Stabilized inverse probability of treatment weighting (sIPTW) was used to balance baseline patient characteristics.
RESULTS: Of 779 eligible patients, 296 received palbociclib+AI and 483 received AI alone as 1L treatment. After sIPTW, the median follow-up was 23.1 months with palbociclib+AI and 18.2 months with AI alone. Adjusted median OS was longer with palbociclib+AI versus AI alone (sIPTW: 37.6 vs. 25.5 months, HR=0.73 [95%CI, 0.59-0.91]. In multivariable CPH regression, patients treated with palbociclib+AI versus AI alone had a 39% lower risk of death (HR=0.61 [95%CI, 0.48-0.77]).
CONCLUSION: In routine US clinical practice, OS was significantly prolonged with palbociclib+AI versus AI alone in 1L treatment of patients aged ≥65 years with de novo HR+/HER2– mBC, adding to the growing body of evidence on the survival benefit of palbociclib+AI in this patient population.
