BioNTech and DualityBio report DYNASTY-Breast02 results for trastuzumab pamirtecan, with modest PFS improvement, immature survival data and higher ILD incidence.
Written By: Sravani Pamanji, PharmD
Reviewed By: Pharmacally Editorial Team
On October 26, 2026, BioNTech and Duality Biologics (DualityBio) announced topline results from DYNASTY-Breast02 (NCT06018337), a global phase 3 trial evaluating trastuzumab pamirtecan (BNT323/DB-1303) in hormone receptor-positive (HR+)/HER2-low metastatic breast cancer. The trial met its primary endpoint, demonstrating a statistically significant but modest improvement in progression-free survival (PFS) compared with investigator’s choice of chemotherapy. Overall survival (OS) data remained immature at the interim analysis.
The companies also reported a higher incidence of interstitial lung disease (ILD) than in previous trastuzumab pamirtecan trials. Although most cases were grade 1 or 2, severe and fatal events occurred in a small proportion of patients. The companies said the available efficacy and safety findings suggested limited potential benefit in the current treatment landscape and that they would discuss the data before determining next steps.
Trastuzumab Pamirtecan: An Investigational HER2-Targeting ADC
Trastuzumab pamirtecan is a third-generation antibody-drug conjugate (ADC) developed by BioNTech and DualityBio. It targets HER2 and uses a topoisomerase I inhibitor-based payload, incorporating DualityBio’s proprietary Duality Immune Toxin Antibody Conjugates (DITAC) platform.
The drug is being investigated in HR-positive/HER2-low metastatic breast cancer, HER2-expressing recurrent endometrial cancer and other advanced or metastatic solid tumours.
DYNASTY-Breast02: Trial Design and Population
DYNASTY-Breast02 was a global, randomised, multicentre, open-label phase 3 trial involving 541 patients with HR-positive/HER2-low metastatic breast cancer. Eligible patients had disease progression after at least two lines of previous hormone therapy or within six months of first-line hormone therapy combined with a CDK4/6 inhibitor in the metastatic setting.
HER2-low expression was defined as immunohistochemistry (IHC) 1+ or IHC 2+ with negative in situ hybridisation (ISH). Participants had not previously received chemotherapy in the metastatic setting.
Patients were randomised 1:1 to receive trastuzumab pamirtecan or investigator’s choice of single-agent chemotherapy: capecitabine, paclitaxel or nab-paclitaxel. PFS was the primary endpoint, with OS as a key secondary endpoint.
Efficacy: Statistical Significance Does Not Establish Clinical Benefit
Meeting the primary endpoint establishes that trastuzumab pamirtecan demonstrated a statistically significant PFS improvement in the trial population. However, the companies characterised the benefit as modest, and the topline announcement did not disclose median PFS in either group, the hazard ratio, confidence intervals or the absolute difference between treatment arms.
Without these numerical results, the magnitude and precision of the treatment effect cannot be independently assessed. Statistical significance alone also does not establish whether the improvement is clinically meaningful relative to available treatment options.
OS data were immature at the interim analysis. Consequently, the findings do not establish whether the PFS improvement will translate into longer overall survival. Detailed results will be needed to clarify the magnitude of benefit and its relevance to patients.
Safety: Higher ILD Incidence Requires Further Assessment
ILD occurred more frequently in DYNASTY-Breast02 than in previous trastuzumab pamirtecan trials. Most reported cases were grade 1 or 2, but severe and fatal events, classified as grade 3–5, occurred in a small proportion of patients.
The companies reported that the overall safety profile was otherwise consistent with previous trials, with no new safety signals. However, the topline announcement did not provide detailed ILD incidence figures or a comprehensive breakdown of events by severity.
This limits assessment of the absolute pulmonary risk and its implications for treatment decisions. The increased incidence, particularly alongside severe and fatal cases, warrants closer examination when interpreting the efficacy findings.
Development Programme and Clinical Implications
BioNTech and DualityBio are evaluating trastuzumab pamirtecan in three ongoing clinical trials:
DYNASTY-Breast02 (NCT06018337): Phase 3 trial in HR-positive/HER2-low metastatic breast cancer.
FERN-EC-01 (NCT06340568): Phase 3 trial in previously treated patients with HER2-expressing advanced recurrent endometrial cancer.
NCT05150691: Phase 1/2 trial in patients with advanced or metastatic solid tumours.
The companies have not announced a final development decision following the DYNASTY-Breast02 findings. The implications for other indications remain uncertain, and the breast cancer results should not be directly extrapolated to different tumour types or treatment settings.
Overall, DYNASTY-Breast02 met its primary PFS endpoint, but the modest improvement, immature OS data and higher ILD incidence leave trastuzumab pamirtecan’s clinical value uncertain. The companies’ assessment of limited potential benefit highlights the importance of evaluating the complete efficacy and safety dataset against existing treatment options, rather than interpreting the primary endpoint in isolation.
References
DualityBio and BioNTech Announce Topline Results of the DYNASTY-Breast02 Global Phase 3 Clinical Trial Evaluating Trastuzumab Pamirtecan in HR+/HER2-low Metastatic Breast Cancer, Duality Bio, 26 October 2026
A Study of DB-1303/BNT323 vs Investigator’s Choice Chemotherapy in HER2-Low, Hormone Receptor Positive Metastatic Breast Cancer (DYNASTY-Breast02), ClinicalTrials.gov ID NCT06018337
About the Writer
Sravani Pamanji is a PharmD (LinkedIn) professional with experience in scientific writing, medical literature review, drug profile preparation, and clinical case documentation. She has contributed to scientific publication and presented at the 74th Indian Pharmaceutical Congress. Her training includes ICH GCP E6(R3), scientific research, and medication safety. She is passionate about evidence-based medical communication and accurate dissemination of clinical and pharmaceutical information.