MSD and Daiichi Sankyo have initiated the Phase III HERTHENA-Breast04 clinical trial, with the first subject receiving a dose of the HER3-directed DXd antibody drug conjugate (ADC), patritumab deruxtecan (HER3-DXd), for breast cancer.
The study is designed to evaluate the therapy in subjects with unresectable, locally advanced or metastatic hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative breast cancer.
US Tariffs are shifting - will you react or anticipate?
Don’t let policy changes catch you off guard. Stay proactive with real-time data and expert analysis.
By GlobalDataThis randomised, open-label trial aims to evaluate the safety and efficacy of the 5.6mg/kg ADC as a single agent in comparison to standard therapies chosen by investigators for this patient group.
Discovered by Daiichi Sankyo, the ADC is being co-developed with MSD.
The companies noted that, for the trial, subjects must not be candidates for additional endocrine therapy and must not be given chemotherapy or an ADC for advanced or metastatic disease.
They must also have experienced disease progression during or within two years of completing adjuvant endocrine and CDK4/6 inhibitor therapy.
The trial will involve a 1:1 randomisation of subjects to receive either patritumab deruxtecan or the investigator’s treatment choice, with stratification based on HER2 expression, treatment intent, HER3 expression levels, and the presence of visceral disease.
Its dual primary goals are overall survival and progression-free survival, as assessed by blinded independent central review.
The trial’s secondary goals are safety, objective response rate, and duration of response.
Approximately 1,000 individuals across North America, Asia, South America and Europe are expected to be enrolled in the study.
Daiichi Sankyo therapeutic area oncology development head Mark Rutstein said: “Despite significant development in the treatment landscape, HR positive, HER2-negative metastatic breast cancer is a highly complex and challenging disease with an overall poor prognosis.
“The promising clinical activity observed in our early phase studies, including ICARUS-Breast01, suggests that patritumab deruxtecan has the potential to become a meaningful new treatment option for this specific type of breast cancer.”
In June 2025, the companies announced first subject dosing in the IDeate-Prostate01 Phase III trial of I-DXd to treat docetaxel in those with metastatic castration-resistant prostate cancer.
ADC content on Pharmaceutical Technology (Or Clinical Trials Arena) is supported by Syngene. Editorial content is independently produced and follows the highest standards of journalistic integrity. Topic sponsors are not involved in the creation of editorial content.
