Abstract PO2-05-06: Palbociclib in advanced hormone receptor positive breast cancer: A real world study in South America

Abstract BACKGROUND: First-line combined endocrine therapy is the standard of care for hormone receptor-positive (HR+) human epidermal growth factor receptor 2 (HER2)-negative advanced breast cancer (ABC). Palbociclib, in combination with aromatase inhibitors or fulvestrant, is a treatment option for HR+/HER2-negative ABC patients. We aimed to analyze the real-world experience of palbociclib in this setting in South America. METHODS: Real-world study collecting sociodemographic and clinical data from women with ABC treated with palbociclib in centers from Chile (n = 40), Perú (n = 61), and Ecuador (n = 10). Treatment efficacy and safety were analyzed. RESULTS: The median age was 54 years (range: 28 – 83), and 81.1% of women had received previous treatment: adjuvant therapy (20.0%), ABC treatment (31.1%), or both (48.9%). The median duration of palbociclib treatment was 14 months (range: 1 – 57), with differences among countries (longer in Perú; p = 0.009). The dose was reduced in 28.2% of women and only 6.5% returned to the previous one. Most women (97.3%) received combined endocrine therapy, letrozole (48.1%) or fulvestrant (44.4%), with differences between countries (p 0.001). Palbociclib was usually the first-line therapy in Ecuador (60.0%) and Perú (80.3%), and the third line in Chile (37.5%). Considering all women, it was the first- or second-line therapy for 52.3% and 20.7% of them, respectively. The overall response rate was 34.2% and progressive disease was significantly lower in patients receiving first-line palbociclib (25.9 vs. 66.0%, p 0.001). The disease-free survival was longer than 12 months in 67.2% of patients treated with first-line palbociclib. Regarding safety, 38.7% of women had any relevant adverse event (AE) during the treatment, most frequently neutropenia (39.5%), diarrhea (9.3%), and elevated transaminase levels (4.7%). The number of patients who developed any relevant AE was lower among the first-line treated patients (19.0% vs. 60.4%, p 0.001). CONCLUSION: The study reflects differences among countries in routine palbociclib use. But considering all data, palbociclib has confirmed its efficacy and safety, supporting its use in HR+/HER2-negative patients, especially as a first-line therapy. Citation Format: Cesar SÁNCHEZ, Suraj Samtani, Henry Gómez, Silvia Falcon-Lizaraso, René Muñoz, Tannia Soria. Palbociclib in advanced hormone receptor positive breast cancer: A real world study in South America 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 PO2-05-06.