Abstract PS4-20: Low levels of interleukin-6 at baseline were significantly associated with improved overall survival of patients treated with eribulin for locally advanced or metastatic breast cancer
(Background)Eribulin, a non-taxane inhibitor of microtubule dynamics, is a unique chemotherapy agent for locally advanced or metastatic breast cancer (MBC). The treatment has been demonstrated to extend overall survival (OS) without extending progression-free survival (PFS). This effect seems to result from the suppression of epithelial-mesenchymal transition (EMT) and improvement of the hypoxic microenvironment by vascular normalization induced by eribulin, directly or indirectly. In a previous study, we identified that high absolute lymphocyte count (ALC) at the baseline was significantly associated with longer OS in the eribulin group, but not in the treatment of physician’s choice (TPC) group, in the phase III EMBRACE trial (Miyoshi et al., Breast Cancer, 2020). These results strongly suggest an association between eribulin efficacy and immune response. Therefore, we focused on serum levels of immune and inflammatory cytokines,which are expected to have greater utility as a predictive factor for eribulin than ALC. Interleukin (IL) 6, an inflammatory cytokine associated with cancerprogression, and soluble interleukin-2 receptor (sIL-2R), a receptor of IL-2 released from various immune cells including T cells, B cells, and natural killer cells, were selected for the investigation. (Patients and methods)A total of 44 patients treated with eribulin for MBC were recruited for the study. We examined the predictive values of IL-6 and sIL-2R in addition to the neutrophil-to-lymphocyte ratio (NLR) and ALC at baseline. The cutoff values of NLR and ALC were set at 3.0 and 1500/μL, respectively. We used the normal ranges of IL-6 (4.0 pg/mL) and sIL-2R (474 U/mL) as cutoff values. (Results)The OS of patients with low NLR (n=28) and high ALC (n=17) were significantly longer than that of patients with high NLR (n=16, p=0.0287) and low ALC (n=27, p=0.0234). There were no significant associations between PFS and NLR or ALC (p=0.0852 and p=0.2231, respectively). Patients with normal IL-6 levels (n=17) had significantly longer PFS (p=0.0023) and OS (p=0.0013) than those with elevated IL-6 levels (n=27). Regarding sIL-2R, patients with normal sIL-2R levels (n=18) had longer OS (p=0.0483) than those with elevated sIL-2R levels (n=26), but their PFS was similar (p=0.2435). Multivariate analysis showed that IL-6 levels were only significantly associated with OS (hazard ratio, 0.093; 95% confidence interval, 0.012-0.720; p=0.0106). There was no significant association between IL-6 levels and NLR or ALC. (Conclusion and discussion)Patients treated with eribulin demonstrated a significantly longer OS if their baseline IL-6 levels were within the normal range. This predictive efficacy for eribulin was more accurate than that of NLR or ALC. As there was no significant association between IL-6 levels and NLR or ALC, IL-6 appears to predict whether the tumor microenvironment is favorable or unfavorable for eribulin treatment, mediated through different mechanisms. Therefore, IL-6 levels may be useful for selecting patients who will benefit from the administration of eribulin in terms of improved OS. Citation Format: Ayako Bun, Natsuko Inoue, Yoshimasa Miyagawa, Reiko Fukui, Yukie Fujimoto, Tomoko Higuchi, Atsushi Sata, Hiromi Ozawa, Michiko Imamura, Yasuo Miyoshi. Low levels of interleukin-6 at baseline were significantly associated with improved overall survival of patients treated with eribulin for locally advanced or metastatic breast cancer [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS4-20.