BioNTech Breast Cancer Trial Shows Modest, Statistically Significant Improvement
Key Facts
BioNTech and DualityBio announced on October 26 that the Phase 3 DYNASTY-Breast02 trial met its primary endpoint, showing a statistically significant but modest improvement in progression-free survival among patients with metastatic HR+/HER2-low breast cancer. The study evaluated trastuzumab pamirtecan in patients who had not received chemotherapy for their metastatic disease, after their cancer progressed during hormonal therapy. The companies said improvement in this measure did not mean the treatment’s effect on overall survival was clear; interim data for that secondary endpoint were immature. The available announcement did not include figures for the size of the treatment effect on progression-free survival. The companies also said their assessment of the available efficacy and safety data left open the possibility that the added benefit for patients could be limited given currently available treatment options.
According to BioNTech’s quarterly report filed with the U.S. Securities and Exchange Commission, 541 patients were enrolled in the trial, and progression-free survival was its prespecified primary endpoint. That means 541 is the number of enrolled participants, not necessarily the number of patients underlying the estimate of the reported result; the available statement did not specify the analysis population or provide detailed efficacy figures. In its 2025 annual report, BioNTech had estimated that the trial would enroll about 532 patients and expected interim data in 2026. In May 2026, the company said the expected timing of the data during the year was based on projections of event accrual in the study. The company’s registry also showed an estimated study period from January 2024 to August 2026, with an estimated enrollment of 541 participants.
The study compared the experimental drug with single-agent chemotherapy selected by the investigator from capecitabine, paclitaxel and nab-paclitaxel, according to the National Cancer Institute registry. Enrollment was open to patients whose disease progressed within 6 months of starting first-line treatment for metastatic disease with a combination of hormonal therapy and a CDK4/6 inhibitor, or after receiving at least two prior lines of hormonal therapy, according to BioNTech’s trial registry. The registry required tumors to have low HER2 expression, with an IHC score of 1+ or an IHC score of 2+ with a negative ISH test, and to be hormone receptor-positive. The study design did not allow prior chemotherapy for advanced or metastatic disease. This places the trial result in the context of patients who had not previously received chemotherapy for this disease, with their cancer continuing to progress after hormonal therapy.
Alongside efficacy, the companies highlighted a higher rate of interstitial lung disease compared with earlier studies of the drug. They said “most cases were Grade 1 or 2,” but a small proportion of patients had severe or fatal cases, Grade 3 to 5. The statement did not report case counts or rates, so it provided no numerical measure to compare the size of the risk across studies. The companies paired this signal with their assessment that the potential benefit could be limited in view of currently available treatments for metastatic hormone receptor-positive, HER2-low breast cancer. The existing treatment context includes trastuzumab deruxtecan, which the U.S. Food and Drug Administration label lists for adults with metastatic hormone receptor-positive, HER2-low or HER2-ultralow breast cancer whose disease has progressed after one or more hormonal therapies in the metastatic setting.
The results are part of a broader program for the drug. In September 2025, BioNTech said a separate Phase 3 trial in China involving patients with metastatic or unresectable HER2-positive breast cancer met its primary progression-free survival endpoint at a prespecified interim analysis. That study concerns a different patient group from those in DYNASTY-Breast02 and does not represent the result of the current trial. BioNTech said at the time that DualityBio planned to discuss next steps for a biologics license application with the Center for Drug Evaluation of China’s National Medical Products Administration. On commercial rights, BioNTech said its global rights exclude mainland China, Hong Kong and Macau, where DualityBio retains the rights. Following the announcement of the current breast cancer results, the companies said they would determine the optimal regulatory pathway after evaluating the breast and endometrial cancer data together.