BioNTech and DualityBio report modest Phase 3 win for trastuzumab pamirtecan with higher ILD rate

Primary endpoint met

BioNTech and DualityBio announced on 26 October 2026 that the global Phase 3 DYNASTY-Breast02 trial met its primary endpoint. Trastuzumab pamirtecan beat investigator-selected chemotherapy on progression-free survival in chemotherapy-naive patients with HR+/HER2-low metastatic breast cancer whose disease had progressed on endocrine therapy. The partners called the improvement statistically significant but modest.

The companies did not disclose numerical efficacy results, RTTNews reported. Trastuzumab pamirtecan is not yet approved. Based on the efficacy and safety information available at the data cut-off, the companies said the potential patient benefit is limited in the current HR+/HER2-low metastatic breast cancer treatment mix.

Trial design

The trial enrolled 541 patients with HR+/HER2-low metastatic breast cancer and HER2-low expression (IHC 2+/ISH- and IHC 1+). Their disease had progressed on at least two lines of prior hormone therapy or within six months of first-line hormone therapy plus a CDK4/6 inhibitor in the metastatic setting. Patients had not received chemotherapy. Investigators randomised them 1:1 to trastuzumab pamirtecan or investigator's choice single-agent chemotherapy: capecitabine, paclitaxel or nab-paclitaxel. Progression-free survival was the primary endpoint and overall survival a key secondary. The study was open-label.

Trastuzumab pamirtecan, also known as BNT323/DB-1303, is a third-generation topoisomerase-1 inhibitor-based ADC targeting HER2. DualityBio built it on its DITAC platform, the companies said.

Higher ILD rate

Interstitial lung disease occurred more frequently than in earlier trastuzumab pamirtecan studies, the companies said. Most cases were Grade 1 or 2. Severe and fatal Grade 3 to 5 events occurred in a small proportion of patients. Otherwise the safety profile was consistent with prior trials, and no new safety signals emerged.

ad-hoc-news.de said that with a modest efficacy edge, the ILD finding cannot be relegated to a footnote.

Overall survival immature

Overall survival, a key secondary endpoint, was immature at the interim analysis, the companies said. That leaves no final verdict on whether trastuzumab pamirtecan extends survival. The announcement gave no numerical PFS results, so the size of the modest gain is not public.

Yahoo Finance said the data read as mixed rather than decisive for a market already familiar with strong ADC competitors such as AstraZeneca and Daiichi Sankyo. The companies said the potential benefit is limited in the current treatment mix.

Next steps

BioNTech said it is discussing the full body of trastuzumab pamirtecan data in breast and endometrial cancer with DualityBio to determine next steps, ad-hoc-news.de reported. A regulatory filing has been described as an option, not a decision.

Development continues in three ongoing studies: DYNASTY-Breast02, the Phase 3 Fern-EC-01 trial in HER2-expressing recurrent endometrial cancer, and a Phase 1/2 study in advanced or metastatic solid tumours, the companies said.