An open-label, multicenter, phase 2 study to evaluate the safety and efficacy of BB-1701, a novel antibody drug conjugate (ADC) targeting human epidermal growth factor receptor 2 (HER2), in previously treated patients with HER2-positive (HER2+) or HER2-low unresectable or metastatic breast cancer (BC).
Authors: Bardia Aditya , O'Sullivan Ciara Catherine , Mahtani Reshma L. , Blau Sibel , Abdulla Nihal E. , Ali Azka , Bansal Rani , Meyer Janelle Marie , George Mridula Annette , Han Hyo S. , Pluard Timothy J. , Papish Steven W. , Jones Jason Michael , Rong Yuanxin , Gao Guozhi , Rugo Hope S. 
Published: June 2024

TPS1122 Background: Treatment options for patients (pts) with unresectable or metastatic BC have improved with the development of novel targeted therapies including trastuzumab deruxtecan (T-DXd), an ADC directed against HER2 with a cytotoxic topoisomerase I inhibitor as a payload. Currently, there are limited treatment options for pts with HER2+ or HER2-low metastatic BC that has progressed on T-DXd. BB-1701 is an ADC consisting of a monoclonal antibody targeting HER2 with eribulin (microtubule inhibitor) as a payload that is capable of exerting a bystander effect. A first-in-human dose-finding Study 101 of BB-1701 is ongoing. Here we describe Study 205, an open label, multicenter, phase 2 study of BB-1701 in pts with HER2+ or HER2-low unresectable or metastatic BC who have disease progression after treatment with T-DXd. Methods: Study 205 (NCT06188559) includes dose-optimization and dose-expansion parts for BB-1701. Eligible pts must have histologically confirmed HER2+ or HER2-low, unresectable or metastatic BC, with measurable disease per RECIST v1.1. Prior treatment must include 1–3 prior chemotherapy-based regimens for unresectable or metastatic BC, including T-DXd. The primary objectives of the dose-optimization part include determining the recommended dose (RD) and evaluating safety and tolerability of BB-1701. The RD will be assessed by randomly assigning ~50 pts into 1 of 3 dosing cohorts (1.6 mg/kg on day 1 Q3W, 0.8 mg/kg on days 1 and 8 Q3W, and 1.2 mg/kg on day 1 Q3W; IV) in a 2:2:1 ratio. Randomization will be stratified by HER2 status (HER2+ vs. HER2-low) documented prior to T-DXd treatment. The dose-expansion part will enroll ~85 pts at RD; the primary objective includes evaluating the efficacy of BB-1701 at the RD. In both study parts, secondary objectives include assessment of additional efficacy measures (i.e., duration of response [DOR], progression free survival [PFS], overall survival [OS], disease control rate [DCR], clinical benefit rate [CBR], and time to response [TTR]), and pharmacokinetics. Efficacy endpoints will be assessed per RECIST v1.1 by the investigator during the dose-optimization part or by Blinded Independent Central Review during the dose-expansion part. Safety assessments will consist of recording, monitoring, and grading of adverse events (AEs) based on CTCAE v5.0, AEs of special interest, and serious AEs. In both study parts, exploratory objectives will include evaluation of biomarkers of response to BB-1701 and BB-1701 immunogenicity; other efficacy measures (i.e., PFS on the next line of therapy) and population pharmacokinetics will be analyzed in the dose-expansion part only. Pt enrollment is currently open. Clinical trial information: NCT06188559 .