Prognostic value of neutrophil-to-lymphocyte ratio in patients with breast cancer in Ethiopia: using inverse-probability-weighted regression adjustment.

OBJECTIVES: This study aimed to examine the association between the neutrophil-to-lymphocyte ratio (NLR) and the prognosis of patients with breast cancer (BC) in southern Ethiopia. DESIGN: We conducted a hospital-based retrospective cohort study. SETTING: The study was conducted at Hawassa and Wolaita Sodo University Comprehensive Specialized Hospital. PARTICIPANTS: A total of 492 women with BC diagnosed from January 2020 to December 2022 were enrolled. Follow-up extended from the date of diagnosis until the occurrence of an event (death), loss to follow-up or the study end date. OUTCOME MEASURES: Data were collected using a structured data collection tool through medical record review and exported to Stata V.16 for analysis. Unweighted and weighted Kaplan-Meier survival curves were used to estimate death-free survival time. Inverse-probability-weighted regression adjustment was employed to estimate the association of NLR with time to death. At a statistical significance level of p<0.05, regression coefficients with 95% CIs were reported. RESULTS: The incidence of mortality in patients with BC with a higher NLR was 4.2 (95% CI 3.3 to 5.2) per 100 person-month observation (PMO); it was 1.9 (95% CI 1.5 to 2.4) per 100 PMO for those with a low NLR. When everyone in the population of interest has a low NLR, the average time to death is estimated as 17.2 (95% CI 11.4 to 23.0) months. For women with a higher NLR, the average time to death is estimated as 10.8 (95% CI 8.93 to 12.8) months. For women with a higher NLR, the average time to death was shorter by 6.3 months (coefficient: -6.3, 95% CI -12.5 to -0.082). Furthermore, the effectiveness of exposure to high NLR (ratio of average treatment effect to low NLR potential outcome means) was a 36.7% (95% CI 12% to 61%) reduction in mortality rate. CONCLUSIONS: A high NLR was associated with significantly higher mortality in BC patients, independent of baseline clinicopathological variables. Patients with elevated NLR more often presented with advanced stage disease and distant metastases. These findings indicate that NLR, a simple and accessible biomarker, may help to identify patients at increased risk of poor prognosis.