Abstract P3-01-13: Palbociclib, ribociclib and abemaciclib in real-world data: risk of disease progression on first-line treatment of metastatic breast cancer

Abstract Introduction and objectives: Cyclin dependent kinase (CDK) 4/6 inhibitors along with endocrine therapy (ET) is the standard first-line for endocrine receptor (ER)-positive HER2-negative metastatic breast cancer. Three CDK 4/6 inhibitors have the FDA and EMA approval: abemaciclib, palbociclib and ribociclib. They appear to have notable differences in their pharmacokinetic characteristics and ability to inhibit every cyclin. Nevertheless, the natural history of disease associated with each CDK 4/6 inhibitor remains unclear. The aim of this study is to establish a risk prediction model for disease progression under the different therapeutic regimes and assess whether there are differences in terms of efficacy between them. Methods: This is a retrospective observational study in which patients treated with ET plus abemaciclib, palbociclib or ribociclib as front line for metastatic breast cancer in Virgen del Rocio Hospital between April 2014 and April 2021 were selected. Patients in this population were followed for a period of 36 months. They were studied according to their clinical characteristics and disease outcome using descriptive analysis. The risk of progression was studied by a transversal method using a univariate logistic regression model. Moreover, Kaplan Meier curves were used to estimate progression-free survival (PFS) and the Breslow test to estimate the p value. All statistical analyses were performed with SPSS 28.0 (Statistical Package for the Social Sciences). Results: A total of 189 patients were selected. 55(29.1%) of them received abemaciclib, 83(44%) palbociclib and 51(27%) ribociclib. 50(27%) patients had de novo metastatic disease, while 139(73%) were recurrences of previous disease. Almost half of the patients (45%) received fulvestrant and 104 (55%) patients received aromatase inhibitors. Table 1 represents the proportion of patients with visceral involvement and endocrine resistance in each arm. The univariate logistic regression model showed that patients treated with palbociclib had 2.36(CI95% 1.165-4.765) times the risk of progression compared to abemaciclib, while patients treated with ribociclib had 2.50(CI95% 1.139-5. 475) times the risk of progression compared to abemaciclib. Overall PFS was 30.03 months. A tendency towards best PFS with abemaciclib in comparison with the other CDK 4/6 inhibitors was appreciated, but it did not reach statistical significance (abemaciclib-palbociclib p=0.289; abemaciclib-ribociclib; p= 0.293; palbociclib-ribociclib p=0.979). Conclusions: In our sample of patients with ER-positive HER2-negative metastatic breast cancer treated with the different CDK 4/6 inhibitors as front line therapy, patients with abemaciclib achieved a lower risk of progression and a trend toward longer PFS. Further follow-up will be necessary to determine whether abemaciclib provides greater benefit in PFS. Table 1. Proportion of patients with visceral involvement and endocrine resistance in each arm. Visceral metastases: Liver, Lung, central nervous System; Non-Visceral: Bone, skin, Lymph node. Citation Format: Mónica Cejuela, M. ángeles Castilla, Marta Benavent, Sonia Molina-Pinelo, Maria A Dominguez-Cejudo, Ana Gil, Alejandro Falcon, Francisco Javier Salvador Bofill. Palbociclib, ribociclib and abemaciclib in real-world data: risk of disease progression on first-line treatment of metastatic breast cancer. [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P3-01-13.