Association of neutrophil percentage-to-albumin ratio with distant metastasis and survival outcomes in breast cancer patients: a retrospective and prospective cohort study.

Breast cancer (BC) is the most common malignancy in women worldwide, with distant metastasis being the leading cause of BC-related mortality. The neutrophil percentage-to-albumin ratio (NPAR), reflecting systemic inflammation and nutritional status, has shown prognostic potential in other cancers, but its role in BC remains unclear. We conducted a single-center retrospective and prospective cohort study including 348 invasive BC patients admitted between 2016 and 2023. Baseline NPAR was calculated before treatment. Logistic regression and restricted cubic spline analyses were used to assess associations between NPAR and distant metastasis risk. For metastatic patients, overall survival (OS) was evaluated prospectively through outpatient visits, telephone contact, and review of medical records using Kaplan-Meier curves and Cox regression. NPAR was significantly higher in metastatic than non-metastatic patients [median 15.9 vs. 15.0, P < 0.001]. Each SD increase in NPAR was associated with 65% higher odds of distant metastasis (adjusted OR  1.647, 95% CI 1.275-2.162). Using the cutoff of 17.7, high NPAR predicted a fourfold higher metastasis risk (OR 4.136, 95% CI 2.231-7.961). Among metastatic patients, high NPAR was linked to shorter OS (45 vs. 63 months; log-rank P = 0.036) and doubled mortality risk (HR  2.064, 95% CI 1.022-4.169). Baseline NPAR is an independent predictor of metastasis risk and survival in BC. As a simple, inexpensive, and clinically available biomarker, NPAR may facilitate early risk stratification and guide personalized management.