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Merck, Daiichi withdraw US application for lung cancer ADC after FDA pushback

Merck, Daiichi withdraw US application for lung cancer ADC after FDA pushback

New Capabilities

Second of three ADCs from a $22 billion partnership fails to clear the FDA's accelerated approval bar

September 25th, 2026: BLA voluntarily withdrawn

Overview

Updated Sep 29

Merck and Daiichi Sankyo withdrew their US application for ifinatamab deruxtecan, an experimental antibody-drug conjugate for extensive-stage small cell lung cancer, an aggressive disease that has resisted most new treatments. The FDA had told the companies their Phase 2 data were not enough to support accelerated approval, and the bid was pulled on September 25.

The withdrawal is the second of three ADCs from the companies' $22 billion partnership to be dropped in the US, and it erases an edge they held over rivals. GSK and Roche posted strong survival data for competing drugs this month, and Amgen's treatment was already fully approved in the same setting.

Why it matters

The setback may let GSK and Roche win the race to bring the next lung cancer antibody-drug conjugate to market.

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Key Indicators

2 of 3
Partnership ADCs withdrawn in the US
Patritumab deruxtecan was pulled in 2025; ifinatamab deruxtecan followed in September 2026.
$22B
Potential value of the 2023 partnership
Merck and Daiichi Sankyo's deal covers three antibody-drug conjugates.
$4B
Upfront commitment in the 2023 deal
Merck paid Daiichi Sankyo $4 billion upfront to partner on the three ADCs.
48.2%
Confirmed response rate in Phase 2
Objective response rate from IDeate-Lung01; median duration of response was 5.3 months.
Oct 10, 2026
Original FDA action date
Decision deadline the withdrawal preempted.

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People Involved

Abderrahmane Laadem
Abderrahmane Laadem
Head of therapeutic area oncology development at Daiichi Sankyo
Overseeing the ongoing Phase 3 program for ifinatamab deruxtecan
MG
Marjorie Green
Senior vice president and head of oncology, global clinical development at Merck Research Laboratories
Leading Merck's oncology development for the partnership's ADCs
 Levi Garraway
Levi Garraway
Chief medical officer of Roche
Pushing Roche's competing ADC tambotatug pelitecan toward global studies

Organizations Involved

Merck & Co.
Merck & Co.
Pharmaceutical company
Co-developer of ifinatamab deruxtecan

US pharmaceutical giant co-developing three Daiichi Sankyo antibody-drug conjugates.
Daiichi Sankyo
Daiichi Sankyo
Pharmaceutical company
Co-developer and originator of the ADC technology

Japanese drugmaker behind the deruxtecan antibody-drug conjugate class.
U.S. Food and Drug Administration
U.S. Food and Drug Administration
Federal regulator
Found the Phase 2 data insufficient for accelerated approval

US regulator that reviews drug applications and sets approval standards.
GSK (GlaxoSmithKline)
GSK (GlaxoSmithKline)
Pharmaceutical Company
Competitor developing the ADC risvutatug rezetecan

British drugmaker partnering with Hansoh Pharma on the B7-H3 ADC ris-rez.
Amgen Inc.
Amgen Inc.
Biopharmaceutical company
Competitor with an already-approved SCLC treatment

US biotech whose Imdelltra (tarlatamab) is fully approved in the same lung cancer setting.

Timeline

October 2023 September 2026

8 events Latest: September 25th, 2026 · 2 months ago
Tap a bar to jump to that date

  1. BLA voluntarily withdrawn

    Latest Regulatory

    Merck and Daiichi pull the accelerated approval application after the FDA says Phase 2 data fall short.

  2. GSK-partnered rival posts strong survival data

    Competitor

    At WCLC 2026, ris-rez shows 18.5-month median overall survival versus 10.3 months for standard care in China.

  3. FDA accepts application, sets action date

    Regulatory

    FDA accepts the BLA for accelerated approval review with an October 10, 2026 PDUFA date.

  4. FDA lifts the clinical hold

    Regulatory

    Hold lifted after companies tighten eligibility criteria and add safety monitoring.

  5. FDA puts Phase 3 trial on clinical hold

    Regulatory

    Agency halts IDeate-Lung02 after a higher-than-expected incidence of fatal interstitial lung disease.

  6. Amgen's Imdelltra wins full approval

    Competitor

    FDA upgrades Imdelltra to full approval in post-platinum extensive-stage small cell lung cancer.

  7. Phase 2 data show strong response rate

    Clinical Data

    IDeate-Lung01 trial shows 48.2% confirmed objective response rate in extensive-stage small cell lung cancer.

  8. Merck and Daiichi announce ADC partnership

    Deal

    The companies agree to co-develop three Daiichi Sankyo antibody-drug conjugates in a pact worth up to $22 billion.

Scenarios

1

Phase 3 succeeds; I-DXd refiles for FDA approval

Possible Resolves by Q2 2028

Discussed by: Daiichi Sankyo and Merck spokespeople; RBC Capital Markets

Enrollment in IDeate-Lung02 is nearly complete. If the trial shows an overall survival benefit over chemotherapy without an excess of fatal interstitial lung disease, the companies would refile, this time seeking full rather than accelerated approval. Daiichi's Laadem explicitly framed the withdrawal as a step toward that filing.

2

IDeate-Lung02 disappoints; the drug is dropped in SCLC

Possible Resolves by Q2 2028

Discussed by: RBC Capital Markets; ApexOnco analysis

The deruxtecan warhead that drives the drug's potency also produced fatal lung toxicity, and patritumab deruxtecan, the partnership's first ADC, already failed a late-stage study. If IDeate-Lung02 shows no survival benefit or safety remains a concern, the companies could abandon small cell lung cancer and focus the drug on other tumor types.

3

GSK or Roche wins the SCLC ADC race

Likely Resolves by End of 2029

Discussed by: RBC Capital Markets; BioSpace

GSK's ris-rez posted a 54% reduction in risk of death in a China Phase 3 study, with filings planned for 2028. Roche's tambotatug pelitecan showed a median overall survival of 13.3 months versus 9.4 months and is heading into global trials. Either could reach the US market before an I-DXd refiling.

Historical Context

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

September 2025

Patritumab deruxtecan withdrawal (2025)

Merck and Daiichi Sankyo pulled their US application for patritumab deruxtecan, an anti-HER3 ADC for relapsed EGFR-mutated non-small cell lung cancer, after the drug failed to extend patients' lives in a confirmatory Phase 3 trial.

Then

The first of the partnership's ADCs was dropped from US review before any approval.

Now

Set a precedent for the current withdrawal and raised questions about the $22 billion deal's returns.

Why this matters now

It is the same partnership, the same deruxtecan warhead, and the same withdrawal mechanism: a US application pulled after regulatory scrutiny of the supporting data.

2019-present

Enhertu and the deruxtecan ILD problem (2019-present)

Daiichi Sankyo's Enhertu (trastuzumab deruxtecan), the first drug in the deruxtecan class, won approval in multiple cancers. Its potency came with a carry a boxed warning for interstitial lung disease, a potentially fatal side effect.

Then

Enhertu became a blockbuster despite the safety warning, proving the warhead's efficacy can outweigh its toxicity.

Now

The class-wide ILD risk followed every successor ADC, including ifinatamab deruxtecan, whose Phase 3 trial was halted over just such deaths.

Why this matters now

The efficacy-toxicity tradeoff that shaped Enhertu's career is the same tradeoff the FDA weighed in rejecting ifinatamab deruxtecan's accelerated approval bid.

Sources

(9)
+3
BioPharma Dive Merck & Co. press release BioSpace Reuters ApexOnco Managed Healthcare Executive Fierce Biotech Onclive Insider Monkey