This was a post hoc analysis of data from a previous post-marketing study of eribulin in Japan to confirm whether the baseline ALC is a predictive marker for survival in eribulin-treated patients with breast cancer in Japan. This study aimed to confirm whether the results of the non-Asian, global EMBRACE study  hold true regardless of ethnicity. The details of the original post-marketing study of eribulin have been reported previously [4, 5]. In this multicenter, prospective, post-marketing, observational study in Japan (ClinicalTrials.gov: NCT02371174), patients were enrolled from September 2014 to February 2016 and were followed for a maximum of 2 years.
The scientific and ethical validity of the study design was reviewed by Eisai Co., Ltd. This study was conducted in accordance with the Declaration of Helsinki and Japanese Good Post-Marketing Study Practice (GPSP), an authorized standard for post-marketing surveillance. Under GPSP regulations, approvals from the institutional review boards of each institution or informed consent from participating patients are not mandatory; in practice, some institutions might have obtained approval or informed consent when deemed necessary. The personal data related to this study were managed in compliance with privacy protection laws in Japan.
Eribulin-naïve patients with HER2-negative inoperable or recurrent breast cancer who received eribulin as first-/second-line or as third-/later-line chemotherapy were recruited in each institution in approximately equal numbers (1:1 ratio). Patients with severe bone marrow suppression (defined as a neutrophil count of < 1,000/mm3 or platelet count of < 75,000/mm3), patients with a history of hypersensitivity to eribulin components, and pregnant or possibly pregnant patients were excluded.
In accordance with the package insert, eribulin was administered intravenously at a standard dose of 1.4 mg/m2 for 2–5 min on day 1 (initiation of eribulin treatment; baseline) and day 8 of a 21-day cycle as indicated. The starting dose of eribulin was reduced (1.1 mg/m2) depending on the patient’s condition to prevent toxicity.
In this post hoc analysis, data on patients with available data on the baseline ALC and NLR (details are defined below) were analyzed.
ALC and NLR data
The baseline ALC and NLR were measured using blood samples collected during 7 days before eribulin administration. Data closest to the date of eribulin administration, but before baseline were used in the analysis. NLR was calculated by dividing the absolute neutrophil count by ALC.
OS was defined as the time from the first eribulin administration to all-cause death or the last date on which the patient was known to be alive (censored).
The cut-off value of ALC was set at 1500/μL. A baseline ALC of < 1500/μL was defined as low, and a baseline ALC of ≥ 1500/μL was defined as high, in line with the previous study . The cut-off value of NLR was set at 3. A baseline NLR of < 3 was defined as low, and a baseline NLR of ≥ 3 was defined as high, in line with previous studies [6, 7].
All analyses were performed with data from patients with evaluable baseline ALC and NLR in the effectiveness analysis set in the post-marketing study. The data of patients without baseline blood test data were excluded. The baseline characteristics and eribulin treatment status were summarized descriptively using a baseline ALC cut-off value of 1500/μL and a baseline NLR cut-off value of 3.
First, to analyze the OS according to the baseline ALC or NLR, Kaplan–Meier curves were drawn to depict the survival rates in each group (i.e., ALC ≥ 1500 vs. < 1500/μL and NLR ≥ 3 vs. < 3) and the median OS (95% confidence interval [CI]) was estimated. The survival rates for 6 months, 1, and 2 years were also calculated. The hazard ratios (HRs) and 95% CIs for ALC of ≥ 1500 vs. < 1500/μL, and NLR of ≥ 3 vs. < 3 were estimated using the Cox proportional hazard model.
Although the ALC and NLR may individually be useful immune response markers, the combination of these markers may better predict survival outcomes in patients than each marker alone. Thus, to further examine the OS by combining the baseline ALC and NLR, patients were categorized into four groups: (1) ALC of ≥ 1500/μL and NLR of < 3, (2) ALC of ≥ 1500/μL and NLR of ≥ 3, (3) ALC of < 1500/μL and NLR of < 3, and (4) ALC of < 1500/μL and NLR of ≥ 3. The group of patients with an ALC of ≥ 1500/μL and an NLR of < 3 was used as a reference, and the HRs of the other groups were estimated.
To explore the relationship between ALC and NLR at baseline and the number of chemotherapy regimens for inoperable or metastatic disease prior to eribulin administration, HRs were estimated for ALC of ≥ 1500 vs. < 1500/μL and NLR of ≥ 3 vs. < 3 in each subgroup categorized by the number of chemotherapy regimens.
To explore the potential factors affecting OS, including the baseline ALC and NLR, univariate and multivariate Cox regression analyses were performed. First, HR and 95% CI were calculated for each factor using the univariate model. To further evaluate the factors affecting OS after adjusting for covariates, multivariate Cox regression analysis was performed using the stepwise selection method with a selection criterion of p < 0.20. Factors with p < 0.05 were considered statistically significant. Because the analysis was conducted for exploratory purposes, no adjustments were made for multiple testing. To best replicate the analysis of the potential factors for OS in the EMBRACE study, we planned to include the same factors with the same categories as in the previous study , as long as they were available in our data. Consequently, the following factors were considered in the univariate and multivariate Cox regression analyses: visceral metastasis, age, Eastern Cooperative Oncology Group Performance Status (ECOG PS), number of previous chemotherapy regimens for inoperable or metastatic disease, triple-negative, previous capecitabine treatment, estrogen receptor (ER) status, progesterone receptor (PgR) status, hormone receptor (HR) status, number of involved organs, baseline ALC, and baseline NLR.
Additionally, we also analyzed the OS of eribulin-treated patients using different ALC cut-off values by calculating the median OS and HR with 95% CIs for the high and low ALC groups using cut-off values ranging from 1000 to 1800/µL. This analysis was conducted to confirm whether a consistent trend (i.e., patients with a higher baseline ALC showed a longer OS than those with a lower ALC) was observed when using a different cut-off value instead of determining the optimal cut-off value for Japanese patients. All analyses were performed using SAS software version 9.4 (SAS Institute, Inc., Cary, NC, USA).