Factors Affecting the Survival of Metastatic Breast Cancer Patients Treated With Cdk 4/6 Inhibitors

Objective We aim to determine the efficacy, and the factors associated with the effectiveness of first-line CDK4/6i (ribociclib or palbociclib) in HR-positive, HER2-negative MBC patients. Material and method This is a retrospective, cross-sectional, and descriptive study. Ninety patients with metastatic breast cancer receiving CDK 4/6i from three different oncology clinics were included in the study. Results Of the patients, 56 (62.2%) had received ribociclib, and 34 (37.8%) palbociclib. There was no significant difference between the groups regarding age, gender, comorbidities, ECOG performance status, and menopausal status (p>0.05). The cut-off values for ER, PR, and Ki-67 levels were determined by ROC curve analysis. It was found as 80% for ER level, 50% for PR level, and 30% for Ki-67 level. PFS was significantly longer in patients with ER-level greater than 80% and Ki-67 expression less than 30% in multivariate analysis. Among the patients included in our study, the median PFS was 22.41 months in the patients with only a Ki-67 level of 30% and above, while the median PFS was 17.24 months in the patients with only an ER level of 80% and below. In the patients with a combined ER of 80% or less, and a Ki-67 of 30% or more, the median PFS was 12.42 months (p<0.001). Conclusion This study demonstrated that CDK4/6i therapies had longer PFS in patients with ER levels greater than 80% and Ki-67 expression less than 30%. It is essential to determine which patient group benefits more from first-line CDK4/6is.