Background: This study aimed to investigate whether schedule modification is safe and effective in patients intolerant to the standard eribulin dose and schedule. Methods: Patients with metastatic breast cancer (MBC) treated with both anthracycline and taxane and ≤ 3 prior regimens of chemotherapy for MBC received eribulin at the standard dose and schedule (1.4 mg/m2 on days 1 and 8 of a 21-day cycle) in the first cycle
change of dosing schedule (1.4 mg/m2 on days 1 and 15 of a 28-day cycle) was determined by change in neutrophil count, platelet count, aspartate aminotransferase, alanine aminotransferase, total bilirubin, serum creatinine, and non-hematological toxicity on day 8 of the first cycle or day 1 of the second cycle. Clinical benefit rate (CBR
primary endpoint), time to treatment failure (TTF), overall survival (OS), and safety were evaluated. Results: Of the 88 patients who were enrolled and received standard eribulin therapy in the first cycle, 42 patients were moved to the bi-weekly therapy group and 40 continued standard therapy. In the bi-weekly and standard therapy groups, mean relative dose intensity was 62.7 and 90.9%, CBR was 31.0 and 25.0%, median TTF was 81.5 and 75 days, and OS was 523 and 412 days, respectively. Neither group reported severe adverse events. Conclusion: This is the first study to show that a bi-weekly eribulin schedule is tolerable and has comparable efficacy in patients intolerant to the standard eribulin schedule. Clinical trial registration: University Hospital Medical Information Network (UMIN) Center (ID: UMIN 000008491).