Identifying immune-related predictive factors for post-eribulin therapy in patients with HER2-negative advanced breast cancer- A multicenter retrospective study

Background: In the EMBRACE study, eribulin (ERI) monotherapy improved the overall survival (OS) of patients with HER2-negative advanced breast cancer (HER2-ABC). A post hoc analysis identified the baseline absolute lymphocyte count (ALC) as a predictive marker in the ERI arm. We focused on factors at the termination of treatment that had not been considered previously. Methods: We retrospectively analyzed 370 patients receiving ERI for HER2-ABC between July 2011 and June 2024 across 3 institutions. Clinical data, including the ALC, neutrophil-to-lymphocyte ratio (NLR), and other factors, were extracted from medical records. Statistical analyses included the log-rank test and Cox hazard model. The OS was defined as the survival from the initiation of ERI (OS1) and from the termination of ERI (OS2). Results: In the univariate analysis, the OS1 was longer in patients > 65 years old, ER-positive, and with ALC > 1000/μL at ERI initiation than in others, and the OS2 was longer in ER-positive cases with an ERI time-to-treatment-discontinuation (TTD) > 120 days and ALC > 1000/μL at ERI completion. In the multivariate analysis, ER positivity and baseline ALC > 1000/μL remained associated with a longer OS1. ALC > 1000/μL at ERI completion and an ERI TTD > 120 days remained associated with a longer OS2. In the first-line ERI group, the ALC was maintained during ERI administration, whereas in those who received other treatments, it significantly decreased ( p < 0.001). Conclusion: An ALC > 1000/μL at ERI completion was associated with an improved post-ERI OS. Maintaining the ALC during ERI administration may be associated with a favorable prognosis.