Hormone positive breast cancer is a tumor with high mortality. Combining antihormonal therapy with cyclin dependent kinase 4/6 inhibitors (CDK4/6i) has resulted in longer survival. The effect of inflammatory parameters such as c-reactive protein and c-reactive protein/lymphocyte ratio (CLR) on efficacy and survival in CDK4/6i treatment is unknown. In our study, we aimed to investigate the role of CLR and some parameters in predicting progression-free survival (PFS) with CDK4/6i.ObjectiveHormone positive breast cancer is a tumor with high mortality. Combining antihormonal therapy with cyclin dependent kinase 4/6 inhibitors (CDK4/6i) has resulted in longer survival. The effect of inflammatory parameters such as c-reactive protein and c-reactive protein/lymphocyte ratio (CLR) on efficacy and survival in CDK4/6i treatment is unknown. In our study, we aimed to investigate the role of CLR and some parameters in predicting progression-free survival (PFS) with CDK4/6i.This retrospective cohort study included 78 patients with denovo and recurrent metastatic breast cancer treated with CDK4/6i. Cut off values for the prediction of mortality by various numerical parameter scores were performed by ROC Curve analysis. The effect of clinical variables, inflammatory and histopathological parameters on survival was analyzed by Kaplan-Meier method.MethodsThis retrospective cohort study included 78 patients with denovo and recurrent metastatic breast cancer treated with CDK4/6i. Cut off values for the prediction of mortality by various numerical parameter scores were performed by ROC Curve analysis. The effect of clinical variables, inflammatory and histopathological parameters on survival was analyzed by Kaplan-Meier method.Neutrophil/lymphocyte ratio (NLR) and CLR were statistically significant in predicting mortality (p < 0.05). Ki67 and CLR were correlated with PFS. Age and CLR were correlated with OS (p < 0.05). CLR was statistically significant for both PFS (p = 0.022) and OS (p = 0.006).ResultsNeutrophil/lymphocyte ratio (NLR) and CLR were statistically significant in predicting mortality (p < 0.05). Ki67 and CLR were correlated with PFS. Age and CLR were correlated with OS (p < 0.05). CLR was statistically significant for both PFS (p = 0.022) and OS (p = 0.006).In patients with metastatic hormone-positive breast cancer using CDK4/6i, low CLR and low Ki67 were correlated with longer PFS duration.ConclusionIn patients with metastatic hormone-positive breast cancer using CDK4/6i, low CLR and low Ki67 were correlated with longer PFS duration.