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

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

New Capabilities

The drug beat chemotherapy on progression-free survival, but BioNTech and DualityBio call the gain modest and are weighing next steps in a market Enhertu already holds

5 days ago: BioNTech shares fall 5.06% on limited-benefit update

Overview

Updated Yesterday

BioNTech and DualityBio's Phase 3 breast cancer trial met its main goal, but the result is muted. Trastuzumab pamirtecan delayed tumor growth longer than chemotherapy in 541 patients with hormone receptor-positive, HER2-low metastatic breast cancer, a gain the companies call "statistically significant, yet modest."

Interstitial lung disease, a lung-scarring risk of this drug class, appeared more often than in earlier trials of the drug. Most cases were mild; a small share were severe or fatal. The companies are weighing a regulatory filing, which they call an option rather than a decision, and BioNTech shares fell 5.06% to $86.15 on Nov. 6.

Why it matters

A flagship of BioNTech's cancer pipeline fell short of the bar Enhertu set, narrowing its path in HER2-low breast cancer.

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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 the size of the gain.
Grade 1-2
Most interstitial lung disease cases
ILD occurred more often than in prior trials of the drug; 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.
10.1 vs 6.5
Enhertu median PFS vs chemo, in months
DESTINY-Breast04, the Phase 3 trial that made Enhertu the standard in HER2-low breast cancer (HR=0.51).
12%
Interstitial lung disease with Enhertu
Rate reported for Enhertu in DESTINY-Breast04, with 10% of patients having Grade 1-2 events.
5.06%
BioNTech share decline on Nov. 6
BioNTech traded at $86.15 after the company said the drug's benefit may be limited in HR+/HER2-low breast cancer.

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Organizations Involved

BioNTech
BioNTech
Biopharmaceutical company
Co-developer of trastuzumab pamirtecan; discussing a potential regulatory filing with DualityBio

German biotech co-developing trastuzumab pamirtecan with DualityBio.
DualityBiologics (Suzhou) Co., Ltd.
DualityBiologics (Suzhou) Co., Ltd.
Biotechnology company
Co-developer and platform owner

Chinese biotech whose DITAC platform produced trastuzumab pamirtecan.
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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 and the benchmark for trastuzumab pamirtecan.

Timeline

April 2026 November 2026

3 events Latest: 5 days ago

  1. BioNTech shares fall 5.06% on limited-benefit update

    Latest Market reaction

    BioNTech traded at $86.15 after saying trastuzumab pamirtecan may offer limited benefit in HR+/HER2-low breast cancer. The company said it was discussing filing plans with DualityBio.

  2. DYNASTY-Breast02 meets endpoint, benefit modest

    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.

  3. 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.

Scenarios

1

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.

2

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.

3

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.

4

Endometrial cancer becomes the lead indication for trastuzumab pamirtecan

Likely Resolves by Q2 2027

Discussed by: The Pharma News, BioNTech and DualityBio filings

With the breast cancer result described as modest, the companies lean on HER2-expressing recurrent endometrial cancer, where the Phase 2 cohort met its primary endpoint and a biologics license application was planned for 2026 pending FDA feedback. A filing there would put the drug in front of regulators in a smaller market with less entrenched competition than Enhertu.

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 extended median progression-free survival to 10.1 months from 6.5 months with chemotherapy 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.

Sources

(15)
+9
BioNTech (company press release) DualityBio (company press release) BioPharma Dive Endpoints News Unbiased Headlines The Pharma News Boerse Express BioPharm International Biobook Media ApexOnco ad-hoc-news.de CBA USA News The Pharma Digest Tiger Brokers Flash24