Retrospective registry of patients with locally advanced/metastatic HR⁺/HER2⁻ breast cancer treated in clinical practice in Andalusia.

e13028 Background: In the last years, the cyclin-dependent kinase (CDK)4/6 inhibitors (i) have been used for the treatment of hormone receptor-positive (HR+)/human epidermal growth factor receptor 2-negative (HER2−) Metastatic state of breast cancer (MBC) patients. There is a need for real-world evidence studies on the results obtained with these drugs in which context are being used by the physicians. The aim of this study is to compare the clinical and demographic characteristics of HR+ Her2- MBC patients treated with and without CDK4/6i according to standard clinical practice in Andalusia, a region of Spain, to analyze the current situation of access to CDK4/6i in patients with MBC in Andalusia. Methods: Observational, multicenter, retrospective cohort study of patients with HR+/HER2−MBC treated under clinical practice conditions in the Autonomous Community of Andalusia. The cohorts were defined according to the treatment received in the CDK4/6i group (patients treated with CDK4/6i at first line for advanced disease) or the control group (patients not treated with CDK4/6i for advanced disease). CDK4/6i group patients were treated between November 1, 2017, and April 3, 2020. Patients were followed up during treatment according to the routine practice at each participating center. All patients signed a written informed consent at the time of enrollment. Results: A total of 273 patients participated in the study; of these, 61 patients were not evaluable and were excluded from the analysis. The final number of patients analyzed was 212, with 37 in the control group and 175 in the CDK4/6i group. The comparison of the treatment characteristics between two groups of patients revealed statistically significant differences in several dimensions. The patients treated with CDK 4/6i were found to be younger (p=0.001) and had a disease-free interval (p=0.034) when compared with the control group. They were also more likely to have multiple metastases (p=0.002) and a higher proportion of performed biopsies (p=0.045). The rest of the clinical and demographic factors analyzed did not reach statistical significance. The cohort of patients treated with CDKi achieved a PFS1 of 20.4 months and those not treated with CDKi 12.1 months. The PFS2 of both groups were similar, 6.2 months and 6.6 months for the CDKi-treated and control cohorts, respectively. Finally, the survival rate at 12 and 24 months was 92.9% and 78.4%, respectively. Conclusions: The findings of the study suggest that clinical criteria used in practice lead to CDK4/6i treatment of HR+/HER2−MBC in younger patients with longer disease duration, higher likelihood of multiple metastases, and a higher proportion of biopsies performed. Moreover, CDK4/6i treatment was associated with improved clinical effectiveness compared to the control cohort.