Prevention of New Metastatic Lesions by Eribulin Monotherapy Is Associated with Better Prognosis in Patients with Metastatic Breast Cancer

Background: Eribulin therapy has been reported to prolong overall survival (OS) but not progression-free survival, probably because it prevents the development of metastatic lesions; however, this effect has not yet been confirmed. Methods: We reviewed the medical charts of 50 patients with metastatic breast cancer who underwent eribulin monotherapy at our hospital between 2014 and 2019. Patients were divided into two groups, namely, those who discontinued eribulin because of disease progression due to development of new lesions (NL group) and those who discontinued eribulin for other reasons, such as lesion growth and un-acceptable side effects (non-NL group). Survival times were estimated for both groups and we investigated if eribulin-mediated suppression of new metastasis increased OS. Results: Median OS for all patients, from eribulin initiation, was 14.4 months (range 1.2-60.1), whereas it was 4.6 months (range 1.7-24.7) in the NL group and 16.8 months (range 1.2-60.1) in the non-NL group. OS was significantly poorer in the NL group than in the non-NL group (p < 0.05). Conclusion: Eribulin monotherapy-mediated suppression of new metastatic lesions results in a better prognosis in patients with metastatic breast cancer.