Trastuzumab pamirtecan shows modest benefit in HER2-low breast cancer Phase 3 trial

Overview

Updated 2 hours ago

BioNTech and DualityBio's Phase 3 breast cancer trial met its main goal, but the result is muted. Trastuzumab pamirtecan improved progression-free survival over chemotherapy in 541 patients with hormone receptor-positive, HER2-low metastatic breast cancer. The companies call the gain "statistically significant, yet modest."

Interstitial lung disease, a known risk of this drug class, appeared more often than in earlier trials. Most cases were mild, but a small share of patients had severe or fatal events. The companies say the benefit looks limited in a field Enhertu already dominates, and they will decide next steps after reviewing the data.

Why it matters

Trastuzumab pamirtecan was a flagship of BioNTech's oncology pipeline; a modest Phase 3 result narrows its path in a market Enhertu already dominates.

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Key Indicators

541

Patients randomized in DYNASTY-Breast02

HR+/HER2-low metastatic breast cancer patients randomized 1:1 to trastuzumab pamirtecan or chemotherapy.

Modest

Progression-free survival gain over chemotherapy

Statistically significant but modest; the companies did not disclose exact figures.

Grade 1-2

Most interstitial lung disease cases

ILD occurred more often than in prior trials; a small share of patients had Grade 3-5, including fatal, events.

Immature

Overall survival data at interim analysis

The secondary endpoint was not mature enough to draw conclusions.

Voices

Curated perspectives — historical figures and your fellow readers.

Ever wondered what historical figures would say about today's headlines?

Organizations Involved

BioNTech

Biopharmaceutical company

Co-developer of trastuzumab pamirtecan

German biotech co-developing trastuzumab pamirtecan with DualityBio.

DualityBiologics (Suzhou) Co., Ltd.

Biotechnology company

Co-developer and platform owner

Chinese biotech whose DITAC platform produced trastuzumab pamirtecan.

AstraZeneca / Daiichi Sankyo (Enhertu partnership)

Pharmaceutical partnership

Developer of the approved rival Enhertu

Developers of Enhertu (trastuzumab deruxtecan), the approved standard in HER2-low breast cancer.

Timeline

April 2026 October 2026

2 events Latest: Today

October 2026
DYNASTY-Breast02 meets endpoint, benefit modest
Today Clinical trial result

The global Phase 3 trial met its primary endpoint: trastuzumab pamirtecan improved progression-free survival over chemotherapy in 541 hormone receptor-positive, HER2-low metastatic breast cancer patients. The gain was modest and interstitial lung disease rates were higher than in earlier trials.
Today
April 2026
Endometrial cancer cohort meets its goal
Clinical trial

The Phase 2 cohort of the global Phase 1/2 trial in HER2-expressing recurrent endometrial cancer met its primary endpoint, with results published. A biologics license application is planned this year, contingent on FDA feedback.
April 2026

Scenarios

BioNTech, DualityBio shelve the HER2-low breast cancer program

Likely Resolves by Q2 2027

Discussed by: BioPharma Dive, Endpoints News, Boerse Express

The companies weigh the modest progression-free survival gain and higher lung toxicity against Enhertu's dominance. A formal decision to deprioritize or discontinue the breast cancer program would follow, with focus shifting to endometrial cancer, where a biologics license application is already planned.

Companies push trastuzumab pamirtecan toward a breast cancer filing

Possible Resolves by End of 2027

Discussed by: Endpoints News

Despite the modest result, the companies choose to submit for approval, betting that a second option can capture some market share or that regulators view the benefit-risk as acceptable. This would put the drug directly against Enhertu in the same patients.

Full data reveal benefit in a defined patient subgroup

Possible Resolves by Q2 2027

Discussed by: European Society for Medical Oncology (ESMO) meeting program

Presentation of the full dataset at a medical meeting may show the benefit concentrates in a subset of patients, such as those with higher HER2 expression (IHC 2+) or a biomarker-defined population. The companies could then position the drug for those patients only.

Historical Context

2 moments from history that rhyme with this story — and how they unfolded.

June 2022

DESTINY-Breast04 (2022)

AstraZeneca and Daiichi Sankyo presented Phase 3 data showing their HER2-targeting antibody-drug conjugate Enhertu roughly doubled progression-free survival in HER2-low metastatic breast cancer, a population once excluded from HER2-targeted therapy.

Then

Enhertu was approved and became the standard of care for HER2-low breast cancer.

Now

The trial created a new treatment category and set a high bar for every later entrant.

Why this matters now

Trastuzumab pamirtecan is now measured against this benchmark; its modest benefit and higher lung toxicity look weak by comparison.

February 2013 – 2022

Kadcyla's displacement by Enhertu (2013-2022)

Roche's Kadcyla (trastuzumab emtansine), the first HER2-targeting antibody-drug conjugate, became the standard for HER2-positive metastatic breast cancer after its 2013 approval. Enhertu then showed head-to-head superiority in the DESTINY-Breast03 trial and took over for many patients.

Then

Enhertu displaced Kadcyla as the preferred HER2-targeted antibody-drug conjugate.

Now

The episode shows that in this drug class, a new entrant must clearly beat the incumbent to win the market.

Why this matters now

Trastuzumab pamirtecan's modest result suggests it does not clearly beat Enhertu, the current incumbent, in HER2-low breast cancer.