Abstract PS5-01-03: Jbcrg-m06/emerald post-hoc analysis by physician’s choice of docetaxel or paclitaxel: efficacy and safety of eribulin mesylate vs taxanes combined with trastuzumab and pertuzumab as first-line for her2-positive locally advanced or

Abstract Background The randomized open-label phase 3 JBCRG-M06/EMERALD study (NCT03264547) was the first to show the non-inferiority of eribulin (E) to taxane (T) (docetaxel [DTX] or paclitaxel [PTX]) when combined with dual HER2 blockade as first-line chemotherapy for HER2+ locally advanced or metastatic breast cancer (LABC/mBC) (doi: 10.1200/JCO-24-01888). In the primary analysis results, median progression-free survival (PFS) was 14.0 and 12.9 months (mo) in the E and T groups, respectively (hazard ratio, 0.95). Although median treatment duration was longer with E (28.1 weeks) than with DTX or PTX (18.1 and 20.5 weeks, respectively), incidences of adverse events (AEs) were similar between the E and T groups. While DTX and PTX have some pharmacological similarities, their distinct properties may result in differences in therapeutic outcomes. We report the results of a post-hoc analysis in which outcomes were analyzed by type of T used and compared with those when E was used. Methods Patients (pts) with HER2+ LABC/mBC were randomized to receive E (1.4 mg/m2 on days 1 and 8) or T (DTX 75 mg/m2 on day 1 or PTX 80 mg/m2 on days 1, 8, and 15), intravenously in a 21-day cycle, each with trastuzumab + pertuzumab. In the T group, the choice between DTX and PTX was determined by the attending physician, but it had to be declared in advance at the time of enrolment. The Kaplan-Meier method was used to assess survival outcomes, and the log-rank test for intergroup comparisons. Waterfall and swimmer plots were used to assess outcomes based on type of T used. Results Of the total 446 pts, 224 received E and 222 received T (DTX, n = 186; PTX, n = 36) (intention-to-treat population); 224 in the E group and 218 in the T group (DTX, n = 184; PTX, n = 34) received at least one dose of the study drug (safety analysis population). Baseline characteristics were well balanced between the groups. In the T group, pts treated with DTX or PTX had no differences in age or ECOG performance status. Survival outcomes were similar between pts who received DTX or PTX (Table 1A). Incidences of AEs were generally similar between the E and T groups, regardless of type of T used; however, a higher incidence of peripheral sensory neuropathy was noted with PTX whereas it was lower with DTX, compared with E. Additionally, the incidence of neutropenia tended to be lower with DTX (Table 1B). Conclusions In our trial comparing T and E combined with dual HER2 blockade as first-line treatment for HER2+ LABC/mBC, DTX and PTX were used to treat 84% and 16% of pts, respectively. No differences in efficacy (i.e. non-inferiority results) were observed based on type of T used. While AEs were generally similar between the E and T groups, regardless of type of T used, a higher incidence of peripheral sensory neuropathy was noted with PTX compared with E or DTX. Citation Format: N. Masuda, S. Saji, Y. Kojima, M. Kitada, H. Tada, T. Iwasa, K. Koizumi, H. Shigematsu, Y. Sagara, T. Okuno, Y. Hasegawa, E. Tokunaga, T. Shien, U. Toh, T. Kuwayama, M. Shimoda, H. Hasegawa, S. Morita, T. Yamashita. Jbcrg-m06/emerald post-hoc analysis by physician’s choice of docetaxel or paclitaxel: efficacy and safety of eribulin mesylate vs taxanes combined with trastuzumab and pertuzumab as first-line for her2-positive locally advanced or metastatic breast cancer [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS5-01-03.