Abstract PO1-05-09: ASCENT-07: A phase 3, randomized, open-label study of sacituzumab govitecan versus treatment of physician’s choice in patients with HR+/HER2– inoperable, locally advanced, or metastatic breast cancer post-endocrine therapy

Abstract Background: Approximately 70% of all breast cancer (BC) cases are hormone receptor positive/human epidermal growth factor receptor 2-negative (HR+/HER2–), with ~65% of these being HR+/HER2-low (immunohistochemistry [IHC]1+, IHC2+/in situ hybridization [ISH]–). Despite an increasing number of available endocrine and targeted treatments for metastatic disease, tumors eventually develop resistance to endocrine therapy (ET). Chemotherapy, the standard of care for patients (pts) whose cancers no longer respond to ET, is associated with poor outcomes, representing a high unmet need in the first-line endocrine-resistant setting. Sacituzumab govitecan (SG) is a Trop-2–directed antibody-drug conjugate (ADC) that delivers SN-38 (the active metabolite of the topoisomerase inhibitor irinotecan) to tumor cells via internalization, and to the surrounding tumor microenvironment via the bystander effect. SG demonstrated a significant and clinically meaningful survival benefit in the phase 3, randomized TROPiCS-02 trial, and is approved in the US for inoperable, locally advanced, or metastatic HR+/HER2– BC after ET and ≥ 2 systemic therapies in the metastatic setting. ASCENT-07 will examine the efficacy and safety of SG in the first-line chemotherapy setting, ie, in patients with inoperable, locally advanced, or metastatic ET resistant HR+/HER2– BC. Study design: ASCENT-07 (NCT05840211) is a randomized, open-label, global study evaluating SG versus treatment of physician’s choice (TPC) chemotherapy in pts with HR+/HER2– inoperable, locally advanced, or metastatic BC who have received ET and are eligible for their first chemotherapy for advanced/metastatic disease. Pts aged ≥ 18 years with histologically confirmed HR+/HER2– (HER2 IHC0 or HER2-low [IHC1+, IHC2+/ISH–]) according to ASCO/CAP criteria, measurable disease per RECIST v1.1, and ECOG performance status of 0 or 1 will be included. Pts are eligible if they meet ≥ 1 of the following criteria: progressive disease (PD) in the metastatic setting on ≥ 2 lines of ET (± targeted therapy) (disease recurrence within the first 24 months of starting adjuvant ET is considered a line of therapy), PD within 6 months of first-line ET (± CDK 4/6 inhibitor) in the metastatic setting, or disease recurrence within 24 months of adjuvant ET with CDK 4/6 inhibitor initiation and no longer a candidate for additional ET. PD on the most recent therapy will be documented by CT or MRI per RECIST v1.1. Key exclusion criteria include prior treatment targeting topoisomerase I. Pts will be randomized to SG 10 mg/kg IV on days 1 and 8 of a 21-day cycle or TPC (capecitabine, paclitaxel, nab-paclitaxel). The primary endpoint is progression-free survival (PFS) assessed by blinded independent central review (BICR) per RECIST v1.1 criteria or death from any cause, whichever comes first. Secondary endpoints include PFS (assessed by the investigator), overall survival, objective response rate and duration of response per BICR and investigator, and quality of life (QoL) assessed using the EORTC QLQ-C30 cancer questionnaire (primarily change in the Physical Functioning domain at week 16 and time to deterioration in the Global Health Status/QoL domain). Pharmacokinetics and immunogenicity analyses will be undertaken in pts receiving SG. Incidence of adverse events and serious adverse events, including relationship to study drug(s), will be reported. Laboratory and vital signs will be monitored. ASCENT-07 is currently open for recruitment and requires ~654 eligible pts to provide adequate power for assessment of the primary and key secondary endpoints. Citation Format: Hope Rugo, Javier Cortés, Giuseppe Curigliano, Carlos Barrios, Kevin Punie, Yeon Park, Hiroji Iwata, Alex Young, Xuehan Ren, Pelin Cinar, Komal Jhaveri. ASCENT-07: A phase 3, randomized, open-label study of sacituzumab govitecan versus treatment of physician’s choice in patients with HR+/HER2– inoperable, locally advanced, or metastatic breast cancer post-endocrine therapy [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO1-05-09.