Abstract P5-01-10: Clinical and pathologic factors associated with progression-free survival in patients with metastatic hormonal breast cancer treated with ICDK4/6

Abstract Background: Breast cancer (BC) is the most frequent malignant tumor worldwide. The most frequent immunophenotype is luminal. 8-13% are diagnosed in metastatic stages and it is estimated that up to 20-40% of patients in local and locally advanced stages will recur. The first line of treatment in this scenario is cyclin-dependent kinase inhibitors 4 and 6 (ICDK4/6). However, in our setting real world evidence is poor. Methods: We conducted an observational, retrospective, descriptive, cohort study in which women >18 years with histological confirmation of breast cancer with hormone receptors (HR+) and HER-2 negative (-) in metastatic stage were evaluated at the ABC medical center. The primary objective was to evaluate clinical and pathological factors associated with progression-free survival (PFS). Results: 70 patients were treated with ICDK4/6, 54 (77%) presented recurrence while 16 (23%) presented de novo metastases, the median age was 58 years, 52 (74%) women were postmenopausal. The functional status they presented was ECOG 0 (7%), ECOG 1 (50%) and ECOG 2 (43%). Forty-five (64%) received ICDK4/6 in first, 13 (19%) in second, 9 (13%) in third and 3 (4%) in fourth or more lines of treatment. Forty (57%) had HER-2 low. The predominant number of metastatic sites was 2 in 25 (36%). Fifty (86%) used Palbociclib, 6 (9%) Ribociclib and 6 (5%) Abemaciclib. Factors that were associated with greater PFS were: using ICDK4/6 first line 23 vs 15, 20 or 4 months; HR=0.023 [95% CI; 0.004-0.136], p=<0.001; objective response rate (ORR) of 24 vs 6 months, p=0.001; absence of HER-2 low of 25 vs 17 months (p=0.011). Factors associated with longer overall survival (OS) were ORR p=<0.001, ECOG (p=0.019), INL < 4 (p=0.031), lung metastases (p=0.011), liver metastases (p=0.015), other metastatic sites (p=<0.001) and fatigue (p=0.036). HER-2 low status had a trend to lower OS (p=0.059). Adverse events (AE's) G3-4 occurred in 70%, with no differences between ICDK4/6 types, dose adjustments were required in 30%, treatment was discontinued in 19%, The most frequent toxicity with Palbociclib and Ribociclib was neutropenia (72% and 100% respectively), no grade 3-4 toxicities occurred with Abemaciclib. Conclusions: We present a Mexican study with real-world data in luminal breast cancer patients treated with ICDK4/6. PFS, OS, ORR and toxicity are similar to previous reported in clinical trials. Factors associated with higher PFS were the line in which ICDK4/6 was received and ORR. There was no difference between ICDK4/6 types. HER-2 low status appears to be a predictive factor in this setting. Citation Format: Juan Manuel Tovar Cabrera, Alejandro Noguez Ramos, Paula Anel Cabrera Galeana, Raquer Gerson C wilich. Clinical and pathologic factors associated with progression-free survival in patients with metastatic hormonal breast cancer treated with ICDK4/6 [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2024; 2024 Dec 10-13; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2025;31(12 Suppl):Abstract nr P5-01-10.