Treatment Patterns and Clinical Outcomes in Patients with Metastatic Breast Cancer Treated with Palbociclib-Based Therapies: Real-World Data in the Han Population

Abstract

Background: Palbociclib combined with endocrine therapy has become the standard treatment for estrogen receptor-positive (ER+) metastatic breast cancer. However, little is known about the effectiveness of diverse palbociclib-based regimens other than letrozole and fulvestrant in the real-world clinical setting. This study aimed to reveal the treatment patterns and clinical outcomes in Han patients in routine clinical practice. Methods: The clinical data of patients with ER+ metastatic breast cancer treated with palbociclib were collected from the China National Cancer Center database. The efficacy profile of palbociclib in this Han population was evaluated, especially in patients younger than 40 years, in those with bone-only metastasis, for various regimen combinations, and as subsequent systemic therapy. Propensity score matching was employed to match patients with or without previous everolimus treatment. Results: A total of 186 patients from 89 cities in 18 provinces in China were enrolled. Patients older than 40 years (P=0.189), those with metastasis other than bone metastasis (P=0.023), and those who received palbociclib as first-line treatment (P<0.001) had prolonged progression-free survival (PFS) compared with other patients. Median PFS was similar among different palbociclib-combined groups (P=0.566): 10.0 months (95% confidence interval [CI] 3.8–16.1) in the exemestane plus palbociclib group, 9.7 months (95% CI 6.3–13.1) in the letrozole plus palbociclib group, 7.8 months (95% CI 5.5–10.2) in the fulvestrant plus palbociclib group, 7.2 months (95% CI 3.2–11.3) in the toremifene plus palbociclib group, and 6.1 months (95% CI 1.2–11.0) in the anastrozole plus palbociclib group. Patients pretreated with everolimus had significantly worse PFS (3.4 months, 95% CI 0.7–6.1) than those in the everolimus-naïve group (8.8 months, 95% CI 6.6–11.0, P=0.001) in the whole population. After propensity score matching, patients pretreated with everolimus had inferior PFS (4.4 months, 95% CI 0.5–8.2) compared with everolimus-naïve patients (6.1 months, 95% CI 4.7–7.5, P=0.439). Conclusions: Various palbociclib-based regimens have promising efficacy in real-world settings, even in patients with bone-only metastasis. Palbociclib resistance is more common in patients younger than 40 years, in those pretreated with everolimus, and in the settings of subsequent treatment compared with first-line treatment.