Single Center Study: Using Pre-Treatment Neutrophil to Lymphocyte Ratio as a Predictor of Outcome in Metastatic Breast Cancer Patients Treated with Cyclin Dependent Kinase 4/6 Inhibitors

Introduction: Breast cancer is the most prevalent cancer among women worldwide, and prognostic markers are vital for predicting outcomes. Systemic inflammatory markers, such as neutrophil-to-lymphocyte ratio (NLR), lymphocyte-to-monocyte ratio (LMR), and lymphopenia, have been associated with tumor progression and prognosis. This study aimed to assess the predictive effects of NLR, LMR, and lymphopenia in Pakistani women receiving CDK4/6 inhibitors alongside endocrine therapy for metastatic breast cancer. Materials and Methods: We conducted a retrospective study at Aga Khan University Hospital, Karachi, from January 2018 to September 2024. Blood tests conducted within one week before treatment initiation were analyzed for NLR, LMR, and lymphopenia. Results: Among 53 evaluable patients, those with pre-treatment NLR <2.5 had a median progression-free survival (PFS) of 14 months versus 8 months for NLR ≥2.5. Median overall survival (OS) was 24 months (95% CI: 18.4–29.0) for NLR <2.5 and 20 months (95% CI: 14.7–25.2) for NLR ≥2.5. Patients with LMR >3.3 had a median OS of 14 months (95% CI: 9.71–18.29) compared to 12 months (95% CI: 8.4–15.96) for LMR ≤3.3. Lymphopenia patients had a median PFS of 8.0 months (95% CI: 1.78–14.22), while those with normal lymphocyte counts had a PFS of 14.0 months (95% CI: 11.20–16.81). Conclusion: NLR, LMR, and lymphopenia are accessible, cost-effective biomarkers that may aid in prognostication and treatment planning for metastatic breast cancer patients receiving CDK4/6 inhibitors.