BioNTech (NASDAQ: BNTX) and DualityBio (HKEX: 9606) report limited benefit in HER2-low breast cancer
A statistically significant progression benefit came with more lung toxicity, and the partners now describe the drug's potential in this setting as limited.
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BioNTech and DualityBio said their antibody-drug conjugate trastuzumab pamirtecan met the primary endpoint of the Phase 3 DYNASTY-Breast02 trial in HR-positive, HER2-low metastatic breast cancer. The open-label study randomised 541 patients to the drug or investigator's choice of single-agent chemotherapy, and the companies described the improvement in progression-free survival as statistically significant, yet modest.
The release disclosed neither median progression-free survival nor a hazard ratio, and overall survival data were not mature at this interim analysis. The rate of interstitial lung disease was higher than in earlier trials of the drug. Most cases were grade 1 or 2, but grade 3 to 5 events occurred in a small proportion of patients, and no exact figures were given.
Most notably, the partners stated that the available efficacy and safety data suggest the potential benefit to patients would be limited in this treatment landscape. They will discuss the data and determine next steps, and made no mention of a regulatory submission. Such candour is unusual in a topline announcement and should be read as a signal that a filing in this indication is uncertain.
For BioNTech, the result narrows rather than ends the programme. Trastuzumab pamirtecan is also in a Phase 3 study in previously treated HER2-expressing endometrial cancer, and further breast-cancer trials are ongoing. The investment question is whether the asset can show a clearer advantage elsewhere, in a HER2-directed field where established conjugates already set a high bar. Full data, when presented, will be needed to judge the size of the benefit and the extent of the lung-safety concern.