İnvestigation of the relationship between peripheral blood parameters and response to cyclindependent ki̇nase 4/6 (CDK 4/6) inhibitor therapy in metastatic breast cancer

Objective: This study aims to evaluate pre- and post-treatment peripheral blood parameters in patients with metastatic breast cancer receiving CDK4/6 inhibitor therapy and to investigate their association with treatment response. Breast cancer is the most common malignancy among women, and survival significantly decreases at the metastatic stage. CDK4/6 inhibitors (palbociclib, ribociclib, abemaciclib) act by arresting the cell cycle and represent an effective therapeutic option; however, treatment response varies among individuals. In addition to classical tumor markers, novel biomarkers reflecting nutritional and immune status—such as the Prognostic Nutritional Index (PNI)—may be useful in predicting treatment response. Materials and Methods: In this retrospective cohort study, peripheral blood parameters before and after CDK4/6 inhibitor treatment were evaluated in 186 patients diagnosed with metastatic breast cancer and followed at the Gaziantep University Medical Oncology Clinic. The routinely assessed demographic, biochemical, and histological parameters included: age, sex, disease duration, white blood cell (WBC), neutrophil (NEU), lymphocyte (LEU), neutrophil/lymphocyte ratio (NEU/LEU), platelet (PLT), platelet/lymphocyte ratio (PLT/LEU), monocyte (MONO), lymphocyte/monocyte ratio (LEU/MONO), hemoglobin (HGB), C-reactive protein (CRP), albumin, CEA, CA15-3,Calcium,LDH and Prognostic Nutritional Index (PNI). Results:All data were analyzed using IBM SPSS Statistics 23. Depending on data distribution, appropriate parametric (Independent/Paired Samples t-test, One-way ANOVA, Pearson Correlation) or nonparametric (Wilcoxon, Mann–Whitney U, Kruskal–Wallis) tests were applied. The Chi-square test was used for categorical variables, ROC analysis for survival evaluation, and significant variables were further assessed with univariate and multivariate logistic regression. A p-value of <0.05 was considered statistically significant. Conclusion: This study demonstrated that in metastatic breast cancer, response to CDK4/6 inhibitors (palbociclib, ribociclib) is associated with peripheral blood parameters. Specifically, WBC, NEU, NEU/LEU ratio, calcium, CEA, CA15-3, PNI, and albumin values were correlated with treatment response. These findings suggest that inflammatory and immuno-nutritional markers may serve as potential prognostic and predictive biomarkers in CDK4/6 inhibitor therapy. Keywords:Breast Cancer, CDK4/6 inhibitor, Hematological Parameters