Efficacy and safety of palbociclib plus endocrine therapy for patients with HR+/HER2(-) advanced breast cancer in real-world clinical practice

Background: Palbociclib is the first cyclin dependent kinase 4/6 (CDK4/6) inhibitor approved in China to be combined with endocrine therapy (ET) for patients with hormone receptor-positive (HR+)/human epidermal growth factor receptor 2-negative (HER2(-)) metastatic breast cancer. However, palbociclib has only been used in China for a short amount of time, and there is limited data on its real-world applications. This study observed the efficacy and safety of palbociclib plus ET in a real-world setting in southwest China and we hope to provide some references for the treatment of patients with breast cancer in China. Methods: This was an observational study of patients with HR+/HER2(-) advanced breast cancer (ABC) who received palbociclib plus ET. The primary endpoint of the study was progression-free survival (PFS) and the 6-and 12-month progression-free rates. The secondary endpoint included the objective response rate (ORR) and the clinical benefit rate (CBR). Results: A total of 64 patients were enrolled in this study, and 54.7% of them received palbociclib plus ET as the first-line treatment for ABC. The median PFS was 21.6 months (95% CI: 11.2-32.0 months) after a median follow-up period of 13.8 months (95% CI: 11.9-15.7 months). The 6-month progression-free rate was 75.4%, and 48.9% of patients remained progression-free at 12 months. Overall, the ORR was 21.6% and the CBR was 76.5%. Patients with the molecular typing of Luminal A (P=0.035), a lower Ki67 level (P<0.001), sensitivity or acquired resistance to ET (P=0.003), less than 3 visceral metastases lesions (P=0.001), and those who received palbociclib plus ET as first-line or second-line of treatment for ABC (P=0.001) showed longer PFS. A total of 53.1% of patients had grade 3-4 adverse events (AEs), but only 4.7% of patients experienced permanent discontinuation of treatment due to intolerable AEs. Conclusions: The efficacy of palbociclib plus ET is worthy of recognition and the toxicity was acceptable in this study, which is similar to previously reported data from randomized clinical trials and other real-world evidence. Treatment for ABC using palbociclib plus ET should be recommended more widely in China due to the efficacy and safety.