Abstract P2-15-08: Efficacy and possible predictive factors of eribulin in a real-world population of HER-2 negative metastatic breast cancer patients in Japan

Background Eribulin mesylate, a non-taxane microtubule inhibitor, has unique characteristics that modify the tumor microenvironment by reversing epithelial-mesenchymal transition (EMT) to mesenchymal-epithelial transition (MET). These effects might benefit the efficacy of chemotherapies, particularly those administered after eribulin. In fact, the EMBRACE study demonstrated that eribulin did not prolong progression-free survival (PFS) but rather overall survival (OS) when compared to the treatment of physician’s choice (TPC). However, the effects of eribulin on post-eribulin chemotherapy regimens remain unclear. Thus, this retrospective study aimed to assess PFS, OS, and post progression survival (PPS) of women with HER-2 negative metastatic breast cancer (MBC) as real-world data. In addition, clinical and pathological factors were analyzed as predictive factors for the survival measurements. Furthermore, the effect of eribulin on post-eribulin chemotherapies was also evaluated by assessing PFS of post-eribulin chemotherapy compared with PFS of eribulin and PFS of pre-eribulin chemotherapy. Methods A total of 75 women with HER-2 negative MBC who were treated with eribulin between January 2011 and June 2019 were included in this study. PFS, OS, and PPS were calculated according to the Kaplan-Meier method for each patient. The clinical and pathological factors analyzed in this study were hormone receptors, age, number of prior regimens, metastatic site, number of metastatic sites, and hematologic parameters such as neutrophil (NEU) counts, lymphocyte (LYM) counts, and neutrophil to lymphocyte ratio (NLR). A cox model was used to correlate these factors with survivals. In this study, PFS of the post-eribulin chemotherapy cohort divided by PFS of the eribulin-receiving cohort or PFS of the pre-eribulin chemotherapy cohort was analyzed as a unique parameter of the PFS ratio (PFSr, the former was PFSr A and the latter was PFSr B). A PFS ratio of 1.0 or higher may be the significantly favorable effect of eribulin on post-eribulin chemotherapy. Of a total of 75 patients, 46 and 36 were analyzed for assessing PFSr A and B, respectively, since patients who were not eligible for the calculation of PFSr were excluded. Single and multiple regression analyses were used to evaluate the associated factors with PFSr B. Results The median PFS, OS, and PPS were 3.5 months (95%CI 2.5-4.4), 13.1 (95% CI 9.4-16.7), and 13.1(95%CI 9.4-22.9), respectively. In univariate analysis, an age of 65 or older (p=0.001) and lower NLR (p=0.003) were associated with longer PFS. In multivariate analyses, an age of 65 or older (p=0.041) and lower NLR (p=0.008) were associated with superior PFS. NEU counts lower than 4500 (p=0.0028) and lower NLR (p=0.003) were correlated with longer OS in both univariate and multivariable analyses. There were no correlating factors with PPS. The median PFSr A and B were 0.86 and 0.65, respectively, and the percentages of PFSr A and B were 43% and 33%, respectively. Single and multiple regression analysis each showed that none of the factors are correlated with PFSr B. Conclusion The median PFS and OS in our study were comparable to those reported in the EMBRACE study which were 3.7 and 13.1 months, respectively. Age and NLR were associated with PFS and NEU count and NLR was associated with OS. The correlation of NEU count and NLR with PFS and OS suggests that the effects of eribulin might be diminished by a high inflammatory state but enhanced by higher oncologic immune status. In terms of eribulin’s effect on post-eribulin chemotherapy, no conclusive data were obtained in this study, and a larger number of patients should be analyzed. Citation Format: Sera Satoi, Hiroyuki Takei, Keiko Yanagihara, Tomoko Kurita, Maki Nakai, Meishi Hankyo, Rina Kanamaru, Ai Sato. Efficacy and possible predictive factors of eribulin in a real-world population of HER-2 negative metastatic breast cancer patients in Japan [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P2-15-08.