In conclusion, in this post hoc analysis of a real-world post-marketing observational study in Japan, patients with HER2-negative advanced breast cancer receiving eribulin with a baseline ALC of ≥ 1500/μL and an NLR of < 3 showed prolonged OS as compared to those with an ALC of < 1500/μL and an NLR of ≥ 3. Here, ERBB2 is linked to breast cancer.