Abstract
e12529 Background: Eribulin mesylate (eribulin) showed antitumor activity via the anti-tubulin effect, and improved overall survival (OS) in HER2-negative (HER2-) metastatic breast cancer (MBC) patients without extending progression-free survival (PFS) in a phase 3 trial. On the other hand, according to the published data (Watanabe J, Springerplus, 2015), eribulin monotherapy improved OS in the clinical setting, and PFS is a possible surrogate for OS in HER2-, hormone receptor-positive (HR+) MBC patients. However, there is no practical biomarker for PFS in relation to eribulin monotherapy in patients with HER2-HR+MBC. Methods: Eribulin was administered according to the instructions in the package insert (1.4mg/m2 on days [D] 1 and 8, and a 21-day cycle [C]). The medical records of the patients who received eribulin monotherapy were reviewed. Results: From August 2011 to December 2016, 90 HER2-HR+MBC patients received eribulin monotherapy as daily practice at our institution, and 84 (93.3%) patients terminated their therapy. Lung and/or liver metastasis was observed at the induction of the therapy in 68 (86.7%) of the patients. The median relative dose of eribulin on C1D1 was 95.3% (1.33mg/body). Fever was observed during C1 in 23 (25.6%) patients, and grade (G) 3/4 neutropenia was observed on C1D8 in 28 (31.1%) patients. In contrast, only 4 (4.4%) patients developed febrile neutropenia within C1. Due to the delayed recovery of neutrophils, the second cycle of treatment was suspended in 8 (8.9%) patients. With regard to liver test abnormalities, an elevation of one grade in comparison to baseline, which resolved afterward without specific treatment, was observed during C1 in 24 (26.7%) patients. A multivariate Cox regression analysis revealed that G3/4 neutropenia on C1D8 and a delay of C2D1 were strong predictors of PFS (hazard ratio [HR] 0.53; p < 0.05, HR 0.42; p < 0.05, respectively). A chi-squared test revealed no statistically significant differences between the two subgroups in the relative dose on C1D1. Conclusions: This retrospective, observational study revealed that early-onset neutropenia-related events may be a biomarker for eribulin therapy that can be applied in the clinical setting.
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