The efficacy and safety of palbociclib combined with endocrine therapy in patients with hormone receptor-positive HER2-negative advanced breast cancer: a multi-center retrospective analysis

To explore the efficacy and safety of palbociclib combined with endocrine therapy (ET) in advanced breast cancer (ABC). We conducted a retrospective study involving patients with hormone receptor-positive (HR+) and human epidermal growth factor receptor 2-negative (HER2-) ABC who received palbociclib combined with ET in the first- to third-line at three centers in China between January 2018 and October 2020. A total of 151 patients were included in this study. The median age of the patients at palbociclib initiation was 56 years (range 30-86 years) with a median follow-up of 10.9 months (range 2.0-41.2 months). Among these patients, 88 patients received palbociclib combined with ET as first-line therapy, and achieved a median progression-free survival (mPFS) of 19.8 months and an objective response rate (ORR) of 40.9%, meanwhile, in the first-line setting, 62 patients received palbociclib at an initial dose of 125 mg, achieving a mPFS of 20.9 months and an ORR of 46.8%. There were 39 and 24 patients who received palbociclib combined with ET as second- and third-line therapy, the mPFS were 10.0 months and 6.1 months, respectively. The most common and serious adverse events (AEs) were leukopenia and neutropenia. A total of 64 patients (42.4%) underwent palbociclib dose reduction due to AEs. Palbociclib combined with ET is an effective therapeutic regimen for HR+/HER2- ABC, particularly in the first-line setting with palbociclib initial dose of 125 mg, and AEs were manageable.