Abstract OT2-26-01: Open-label, multinational, multicenter, phase 3b/4 study of trastuzumab deruxtecan (T-DXd) in patients with or without baseline brain metastasis with previously treated advanced/metastatic human epidermal growth factor receptor 2-positive breast cancer (HER2+ BC): DESTINY-Breast12

Background: HER2+ BC is associated with a high incidence (up to 50%) of brain metastasis (BM) despite advances in treatment (Zimmer AS et al. Cancer Rep (Hoboken). 2020;e1274; Hurvitz SA et al. Clin Cancer Res. 2019;25:2433-2441). Although several agents have been studied in patients (pts) with HER2+ BC with BM, an unmet medical need remains due to the poor prognosis in this pt population. In DESTINY-Breast01, T-DXd demonstrated efficacy in the overall population and preliminary efficacy in a pt subgroup with stable BM, with a confirmed objective response rate (ORR) of 61.4% and an extracranial confirmed ORR by independent central review (ICR) of 58.3%, respectively, median progression-free survival (PFS) of 19.4 and 18.1 mo, respectively, and median duration of response (DOR) of 20.8 and 16.9 mo, respectively (Modi S et al. Cancer Res. 2021. Abst PD3-06; Jerusalem G et al. Ann Oncol. 2020. Abst 138O). Here we describe a trial evaluating T-DXd in pts ± BM with previously treated advanced/metastatic HER2+ BC. Trial design: DESTINY-Breast12 (NCT04739761) is an open-label, multicenter, international (86 sites in the US, Europe, Australia, and Japan), phase 3b/4 study assessing the efficacy and safety of T-DXd 5.4 mg/kg q3w in pts with HER2+ BC ± BM. Pts will be enrolled in 1 of 2 cohorts (250 pts each): cohort 1 (−BM at baseline) and cohort 2 (+BM at baseline). Pts must have previously treated advanced/metastatic HER2+ BC that has progressed with ≥1 prior anti-HER2-based regimen and received ≤2 lines of therapy in the metastatic setting (excludes pts with prior tucatinib). Pts with BM must have untreated BM not needing immediate local therapy or previously treated stable or progressing BM. Primary endpoints are ORR in cohort 1 and PFS in cohort 2 (both by RECIST version 1.1 per ICR). Secondary endpoints in both cohorts are OS, DOR, time to progression, duration of subsequent therapy, PFS2, safety, and changes in symptoms, functioning, and QOL. Incidence of new symptomatic CNS metastasis (CNSM) is a secondary endpoint in cohort 1, and ORR and CNS ORR by RECIST 1.1 per ICR, CNS PFS and DOR, and time to new CNSM are secondary endpoints in cohort 2. Citation Format: Nancy U Lin, Eva Ciruelos, Guy Jerusalem, Volkmar Müller, Naoki Niikura, Giuseppe Viale, Emma Oscroft, Shawn Anand, Graham Walker, Nadia Harbeck. Open-label, multinational, multicenter, phase 3b/4 study of trastuzumab deruxtecan (T-DXd) in patients with or without baseline brain metastasis with previously treated advanced/metastatic human epidermal growth factor receptor 2-positive breast cancer (HER2+ BC): DESTINY-Breast12 [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr OT2-26-01.