BioNTech and DualityBio report modest Phase 3 win for trastuzumab pamirtecan in HR+/HER2-low breast cancer

What's the deal? BioNTech and Duality Biologics announced on 26 October 2026 that their Phase 3 trial DYNASTY-Breast02 met its primary goal: the antibody-drug conjugate trastuzumab pamirtecan (BNT323/DB-1303) improved progression-free survival (time without the cancer growing) compared with standard chemotherapy in patients with hormone-receptor-positive, HER2-low metastatic breast cancer. The companies described the benefit as statistically significant but modest , and said the data suggest the potential benefit to patients would be limited in today's treatment landscape; they will discuss the results and decide next steps.

Why it matters: The trial is one of BioNTech and DualityBio's key bets in breast cancer. Trastuzumab pamirtecan is an antibody-drug conjugate — a targeted treatment that delivers a chemotherapy payload directly to cancer cells via a docking protein called HER2 — built on DualityBio's DITAC platform and co-developed by the two companies. Here it was tested in 541 patients whose tumours have low HER2 levels and whose disease progressed on hormone therapy but who had not yet had chemotherapy for advanced disease. Patients received either the drug or the doctor's choice of a single chemotherapy agent (capecitabine, paclitaxel or nab-paclitaxel). At this interim look, the secondary goal of overall survival (how long patients lived) was not yet mature.

Safety: A higher rate of interstitial lung disease (lung inflammation) was seen in this trial than in earlier studies with the drug. Most cases were mild (grade 1–2), but a small proportion were severe or fatal (grade 3–5). Otherwise the safety profile was consistent with prior trials, with no new warning signs.

Read more: BioNTech / DualityBio press release, 26 October 2026