Abstract PO4-05-04: Comparative effectiveness of Palbociclib plus Aromatase inhibitor versus fulvestrant alone as initial endocrine therapy for HR+/HER2- advanced breast cancer in Chinese clinical practice: a real-world study

Abstract Background: In the real world, there are still a large number of HR+/HER2- advanced breast cancer patients receiving initial endocrine therapy with fulvestrant monotherapy in China, especially patients with bone metastases only. It is due to lack of data comparing the effective between Palbociclib combined with AI and fulvestrant monotherapy as initial endocrine therapy. On the other hand, there are economic factors and access issues. According to the National Cancer Center's previous clinical experience, Palbociclib combined with AI is superior to fulvestrant monotherapy in HR+/HER2- advanced breast cancer patients receiving initial endocrine therapy. Therefore, we collected and summarized the previous clinical data in our center to compare the effective of Palbociclib combined with AI and fulvestrant monotherapy for HR+/HER2-advanced breast cancer patients receiving initial endocrine therapy in China. Patients and methods: This is a retrospective real-world study of multicenter studies. It aimed at verifying the effective of Palbociclib combined with AI and fulvestrant monotherapy for HR+/HER2-advanced breast cancer patients receiving initial endocrine therapy in China. A total of 392 patients with ≥3 months of follow-up received Palbociclib plus AI or fulvestrant alone in the first-line setting between April 1, 2015 and February 1, 2023. Stabilized inverse probability treatment weighting (sIPTW) was used to balance baseline demographic and clinical characteristics. Real-world progression-free survival (rwPFS) and overall survival (OS) were analyzed. Results: After sIPTW adjustment, a median follow-up of 37 months (range 34-40) in the Palbociclib group and 59 months (range 56-61) in those taking fulvestrant alone. Palbociclib combination regiment was associated with significantly longer median rwPFS compared to fulvestrant alone (22.0 vs 14.0 months; HR,0.469;95% CI 0.370–0.594, p 0·0001). Median OS was not reached in the Palbociclib group and was 57 months (95% CI 54.0–66.0) in the fulvestrant group(HR,0.666; 95% CI 0.437–1.017, p 0·94). Conclusion: In the real-world population of patients, palbociclib combined with AI endocrine therapy is superior to fulvestrant monotherapy in HR+/HER2- advanced breast cancer patients receiving initial endocrine therapy. PFS and OS before IPTW PFS and OS after IPTW Table patient characteristics Citation Format: Jian Yue, Xue Wang, Jie Ju, Zixiang Yang, Tong Wei, Peng Yuan, Min Gao, Ling Xu, Yin Guan. Comparative effectiveness of Palbociclib plus Aromatase inhibitor versus fulvestrant alone as initial endocrine therapy for HR+/HER2- advanced breast cancer in Chinese clinical practice: a real-world study abstract. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO4-05-04.