Neutrophil-to-lymphocyte ratio at the end of treatment with CDK4/6 inhibitors is an independent prognostic factor for ER-positive HER2-negative advanced breast cancer

Purpose: The aim of this study was to elucidate the clinical significance of peripheral blood biomarkers, including absolute lymphocyte count (ALC) and neutrophil-to-lymphocyte ratio (NLR), at the end of treatment (EOT) with CDK4/6 inhibitors abemaciclib and palbociclib in patients with estrogen receptor-positive human epidermal growth factor receptor 2-negative advanced breast cancer. Methods: We included 67 patients treated with fulvestrant plus abemaciclib or palbociclib. Overall survival (OS) since the EOT with CDK/4/6 inhibitors was compared in relation to the levels of ALC and NLR. The cut-off values of ALC and NLR were set at 1000/μL and 3, respectively. Results: Patients with a high ALC at EOT showed significantly longer OS than those with a low ALC (p = 0.0358). Moreover, patients with a low NLR at EOT showed significantly longer OS than those with a high NLR at EOT (p = 0.0044). Looking at the changes of ALC and NLR between baseline and the EOT, patients with a high ALC both at baseline and at the EOT showed significantly longer OS than others (p = 0.0201). Similarly, patients with a low NLR both at baseline and at the EOT showed significantly longer OS after EOT than others (p = 0.0136). Multivariable analysis revealed that the NLR at EOT (low vs. high) and changes in NLR (low at baseline to low at EOT vs. others) were significant and independent prognostic factors for OS after EOT (p = 0.0337, p = 0.0039, respectively). Conclusion: NLR at EOT with CDK4/6 inhibitors is a significant and independent prognostic marker for patients with ER-positive HER2-negative advanced breast cancer.