Indices of peripheral leukocytes predict longer overall survival in breast cancer patients on eribulin in Japan

Background It was reported that eribulin regulates the tumor microenvironment, including the immune system, by inducing vascular remodeling. Lymphocyte counts are a critical index of immune response in patients. The non-Asian, global EMBRACE study has suggested that baseline absolute lymphocyte count (ALC) may be a predictor of the survival benefit of eribulin in breast cancer patients. We examined whether the baseline ALC is a potential predictor of overall survival (OS) in Japanese patients with HER2-negative advanced breast cancer treated with eribulin. Methods This was a post hoc analysis of data from a post-marketing observational study of eribulin in Japan. The OS by baseline ALC was estimated using the Kaplan–Meier method, with the cut-off value of 1500/μL for ALC. The OS by baseline neutrophil-to-lymphocyte ratio (NLR), a general prognostic index in breast cancer patients, was also estimated, with the cut-off value of 3. Results The median OS was longer in patients with an ALC of ≥ 1500/μL than in those with an ALC of < 1500/μL (19.4 vs. 14.3 months; hazard ratio [HR]: 0.628; 95% confidence interval [CI]: 0.492, 0.801). Patients with an NLR of ≥ 3 showed shorter OS than those with an NLR of < 3 (13.2 vs. 18.8 months; HR: 1.552; 95% CI 1.254, 1.921), and NLR also separated OS in patients with an ALC of < 1500/μL. Conclusions Consistent with the findings of a previous study involving a non-Asian, Western population, our study suggested that baseline ALC may be a predictive factor for the survival benefit of eribulin in Japanese patients.