Merck Begins Phase 3 Trial for New Breast Cancer Treatment HER3-DXd

Merck has launched a Phase 3 clinical trial to evaluate the efficacy of HER3-DXd, its new antibody-drug conjugate, in advanced and complex breast cancer. The study aims to enroll around 1,000 patients across Asia, Europe, North America, and South America. HER3-DXd is a drug-conjugated antibody that binds to an anti-HER3 antibody and a chemotherapy drug, developed in collaboration with Daiichi Sankyo. The trial will test HER3-DXd against standard treatments in patients with advanced or metastatic breast cancer that has progressed despite hormone therapy and initial targeted therapy.

Merck & Co., Inc. (known as MSD outside the United States and Canada) has launched the HERTHENA-Breast04 phase 3 clinical trial to evaluate the efficacy and safety of its investigational antibody-drug conjugate (ADC) patritumab deruxtecan (HER3-DXd) in patients with advanced or metastatic breast cancer. The trial aims to enroll approximately 1,000 patients across Asia, Europe, North America, and South America.

HER3-DXd is a HER3-directed ADC developed in collaboration with Daiichi Sankyo. It consists of a fully human anti-HER3 IgG1 monoclonal antibody attached to a number of topoisomerase I inhibitor payloads (an exatecan derivative, DXd) via tetrapeptide-based cleavable linkers. The trial will test HER3-DXd against standard treatments in patients with advanced or metastatic breast cancer that has progressed despite hormone therapy and initial targeted therapy.

The HERTHENA-Breast04 trial is an open-label, randomized, phase 3 study evaluating the safety and efficacy of HER3-DXd (5.6 mg/kg) monotherapy versus physician's choice of treatment. The primary endpoints are progression-free survival (PFS) by blinded independent central review and overall survival (OS). Secondary endpoints include objective response rate, duration of response, and safety.

The trial is based on promising results from the ICARUS-Breast01 phase 2 trial and a phase 1/2 breast cancer trial published in the Journal of Clinical Oncology in June 2022, where HER3-DXd showed potential in patients with metastatic breast cancer. About 70% of breast cancer cases are HR positive, HER2 negative, and these patients experience poor outcomes if they progress following initial treatment, highlighting the need for additional treatment options [1].

Merck's focus on cancer research is driven by its commitment to discovering innovations that can help patients. The company is pursuing research where scientific opportunity and medical need converge, underpinned by its diverse pipeline of more than 25 novel mechanisms. By addressing barriers to clinical trial participation, screening, and treatment, Merck strives to reduce disparities and ensure patients have access to high-quality cancer care.

References:
[1] https://www.stocktitan.net/news/MRK/herthena-breast04-phase-3-trial-of-patritumab-deruxtecan-initiated-r5rof1c1t9d5.html