Daiichi Sankyo and Merck have withdrawn a United States application for ifinatamab deruxtecan. The move takes a prospective small cell lung cancer treatment out of the American regulatory queue. The companies announced the withdrawal by Business Wire at 4:30pm Eastern on Friday 25 September 2026. Most trade coverage followed on Monday 28 September. The Food and Drug Administration had been due to act by 10 October 2026.
What the two companies withdrew
The application was a Biologics License Application, filed for the agent abbreviated to I-DXd. Merck trades as MSD outside the United States and Canada. The proposed indication covered adults with extensive-stage small cell lung cancer. It applied to patients whose disease progressed on or after platinum-based chemotherapy.
The companies said the package did not clear the bar. Their joint announcement of 25 September 2026 sets out the reasoning. The supporting data “do not satisfy requirements needed to support an accelerated approval for the proposed indication”. That wording covers the Phase 2 IDeate-Lung01 trial. Neither the companies nor the agency identified which requirement was not met. No complete response letter was issued, because the application was pulled first.
Marjorie Green is Senior Vice President and Head of Oncology, Global Clinical Development, Merck Research Laboratories. She said the companies were “disappointed that the current dataset are not supportive of an approval at this time”. Abderrahmane Laadem is Head of Therapeutic Area Oncology Development at Daiichi Sankyo. He said enrolment in the Phase 3 IDeate-Lung02 trial “is near completion”.
An identically worded indication is already approved
The proposed wording matches an indication a rival already holds. Amgen’s Imdelltra (tarlatamab) carries full United States approval in extensive-stage small cell lung cancer. Its label covers adults “with disease progression on or after platinum-based chemotherapy”. The FDA granted that full approval on 19 November 2025.
Tarlatamab reached that point on randomised evidence. The Phase 3 DeLLphi-304 trial enrolled 509 patients and compared it with chemotherapy. Amgen reported a hazard ratio for death of 0.60 (95 per cent confidence interval 0.47 to 0.77). Median overall survival was 13.6 months against 8.3 months.
The regulator describes its accelerated route in its own terms. Its programme page sets out the test in one line. The pathway allows earlier approval of drugs that treat serious conditions “and fill an unmet medical need”. LSDN notes the sequence on the public record. One product gained full approval in that wording. An accelerated application in matching wording was then withdrawn. That is an LSDN reading of dated documents. Neither the agency nor the companies has given a reason. LSDN draws no conclusion about the agency’s reasoning.
The data behind the withdrawn filing
IDeate-Lung01 was a randomised, open-label, two-part Phase 2 trial. It enrolled 187 patients across Asia, Europe and North America. Part one tested 8 mg/kg and 12 mg/kg every three weeks. Part two used 12 mg/kg on the same schedule. The primary endpoint was objective response rate by blinded independent central review.
The primary analysis covered 137 patients treated at 12 mg/kg. Daiichi Sankyo’s primary analysis release reported the results in September 2025. Confirmed objective response rate was 48.2 per cent. The 95 per cent confidence interval ran from 39.6 to 56.9. Median duration of response was 5.3 months. Median progression-free survival was 4.9 months. Median overall survival was 10.3 months. Disease control rate was 87.6 per cent.
The enrolled population sat mostly beyond second line. Of those 137 patients, 32 had received one prior line of therapy. The other 105 had received two or more. The proposed indication carried no equivalent limit. Daiichi Sankyo reported a 56.3 per cent confirmed response rate in the second-line subset.
The safety arm of the same dataset
The same analysis carries findings that cut the other way. Treatment-related interstitial lung disease or pneumonitis affected 12.4 per cent of patients, or 17 people. Four of those cases were grade 3. Two were grade 5, meaning fatal, at 1.5 per cent. Grade 3 or higher treatment-related adverse events reached 36.5 per cent.
The FDA later placed a partial clinical hold on IDeate-Lung02, in December 2025. BioPharma Dive, Fierce Biotech and BioSpace all reported it. The trigger was a higher than expected rate of deaths from interstitial lung disease in that trial. The hold was lifted for the United States on 13 January 2026. The trial remained paused in the European Union at that date.
The disclosure route is worth noting. LSDN found no company press release on that hold as at 28 September 2026. LSDN also found no published statement resolving the European pause. LSDN draws no inference from either absence.
What the confirmatory trial is measured against
IDeate-Lung02 is a Phase 3 trial in relapsed disease. It targets around 540 patients after one platinum-based line. Patients are randomised against physician’s choice of amrubicin, lurbinectedin or topotecan. Those same three agents formed the control arm of DeLLphi-304. Tarlatamab outperformed that comparator set on overall survival.
That overlap matters for how the result will read. LSDN observes that the confirmatory study is measured against an arm a fully approved product has already beaten. The companies have not framed it that way. No head-to-head trial of the two products exists. Other B7-H3 programmes are advancing elsewhere, as LSDN’s earlier report on two Chinese trials set out. Readers weighing the small cell lung cancer treatment options should note that design. The comparison runs against chemotherapy, not against the current American standard.
Small cell lung cancer treatment in England looks different
The available therapy shaping the American picture is licensed in Britain but not funded. The MHRA first authorised tarlatamab on 31 December 2024. Amgen UK announced it on 6 January 2025 as a conditional marketing authorisation. That first British indication reached only third-line use. The label has since broadened.
The current UK summary of product characteristics now sets the indication more widely. It covers adults with small cell lung cancer “with disease progression on or after platinum-based chemotherapy”. The text was last revised on 23 December 2025. That wording is wider than the American label, which is confined to extensive-stage disease. The European Commission approved the product in June 2026.
NICE has not followed the label. NICE technology appraisal TA1091, published on 20 August 2025, covers the narrower group treated after two or more lines. It says tarlatamab “should not be used” there. The committee’s preferred incremental cost-effectiveness ratio was £35,393 per quality-adjusted life year.
No appraisal has caught up with the wider licence. LSDN found none covering the broadened indication as at 28 September 2026. The NICE in-development listing returned an error, so that finding is qualified. NICE has issued no positive recommendation for this small cell lung cancer treatment in any line.
The English picture did shift slightly this month. The MHRA authorised lurbinectedin on 23 September 2026, two days before the withdrawal. That authorisation covers maintenance use with atezolizumab after first-line induction. It does not reach relapsed second-line disease. Amrubicin holds no United Kingdom licence. Topotecan therefore remains the familiar English option after platinum, and the funded small cell lung cancer treatment pathway stays thin.
The affected population is not small. Cancer Research UK reports around 50,200 new lung cancer cases a year in the United Kingdom. That figure covers 2019 and 2021 to 2022. Amgen UK cites Macmillan Cancer Support for small cell disease. It puts that subtype at about 15 per cent of lung cancers. LSDN found no MHRA or European marketing authorisation application for ifinatamab deruxtecan as at 28 September 2026.
The alliance has now withdrawn two American filings
This is the second withdrawal from one collaboration. Daiichi Sankyo and Merck announced the deal on 19 October 2023. It covered three DXd antibody drug conjugates. Terms included 4.5 billion US dollars in upfront payments and 1.5 billion in continuation payments over 24 months. The companies put the total potential value at up to 22 billion US dollars.
The first withdrawal came sixteen months ago. The partners pulled the patritumab deruxtecan application on 29 May 2025. Its confirmatory HERTHENA-Lung02 trial had missed on overall survival. Raludotatug deruxtecan remains in development. So does gocatamig, which the partners added to the alliance in August 2024.
What happens next
The IDeate-Lung02 readout now carries the programme. A future application depends on that randomised result rather than on response rates. Primary completion is guided to 2028. LSDN will track whether the partners file in the United Kingdom or Europe, and by which route. LSDN’s FDA drug approval decisions tracker follows the other oncology decisions due this autumn.
Two questions follow for a British readership. The first is whether NICE revisits tarlatamab once fuller survival data are in hand. The second is whether the English small cell lung cancer treatment pathway gains any funded option after platinum. Until one of those moves, the American and British small cell lung cancer treatment landscapes will keep diverging.
