In a significant step forward for oncology research, the first patient has been dosed in the HERTHENA-Breast04 Phase 3 clinical trial. This trial, a collaborative effort between Daiichi Sankyo and Merckis evaluating the efficacy and safety of an investigational treatment called patritumab deruxtecan (HER3-DXd). The study is enrolling patients with advanced or metastatic hormone receptor (HR) positive, HER2 negative breast cancer whose disease has progressed after previous treatment with endocrine and CDK4/6 inhibitor therapies. This patient population often has a poor prognosis, as a significant number of these patients do not survive five years after diagnosis, highlighting the urgent need for new and effective treatment options.

Patritumab deruxtecan is a specially engineered antibody-drug conjugate (ADC) that targets HER3, a protein broadly expressed in approximately 90% of breast tumors and associated with poor patient outcomes. The drug is composed of a monoclonal antibody that attaches to cancer cells, delivering a potent chemotherapy payload directly to them.

This targeted approach aims to minimize harm to healthy cells while maximizing the therapeutic effect. The initiation of the HERTHENA-Breast04 trial is based on promising results from earlier studies, including ICARUS-Breast01 and a Phase 1/2 trial, which showed encouraging clinical activity in patients with metastatic breast cancer. The trial's primary goals are to measure progression-free survival and overall survival, with secondary endpoints including objective response rate and duration of response.

The HERTHENA-Breast04 trial is a large-scale, open-label, randomized study that will enroll approximately 1,000 patients across Asia, Europe, North America, and South America. Patients will be randomly assigned to receive either patritumab deruxtecan or a treatment of the physician’s choice, which may include various chemotherapy agents or another HER2-directed ADC. The randomization process will be carefully stratified based on factors such as HER2 and HER3 expression to ensure a robust comparison. This trial represents a major commitment by both Daiichi Sankyo and Merck to research innovative and cutting-edge therapies that could significantly improve treatment outcomes for one of the most challenging forms of breast cancer.