Amgen's Imdelltra cuts small cell lung cancer deaths 58% in a Phase 3 trial: 21.1 months vs 12.7

Amgen said Saturday that its lung cancer drug Imdelltra (tarlatamab), added to AstraZeneca's Imfinzi (durvalumab), cut the risk of death by 58% compared with Imfinzi alone in patients with extensive-stage small cell lung cancer. Amgen's release put median overall survival at 21.1 months against 12.7 months. Reuters carried the result on Saturday as well. The full data were presented at the European Society for Medical Oncology congress and, according to Amgen, published the same day in the New England Journal of Medicine.

Markets are closed until Monday. Amgen shares closed Friday at $439.26, down 1.8% on the day, with a market value of about $237 billion and a 52-week range of $288 to $450.98, according to Nasdaq data.

What the trial found

DeLLphi-305 enrolled 563 patients who had finished first-line treatment with Imfinzi plus chemotherapy and had not progressed. Half then received Imdelltra plus Imfinzi, and half received Imfinzi alone. The study is open-label, meaning patients and doctors knew which arm they were in. Amgen sponsored it, with partial funding and the durvalumab supplied by AstraZeneca.

The hazard ratio for death was 0.42 (95% confidence interval 0.32 to 0.54). Amgen described this as an interim analysis, with a median follow-up of about 16 months for survival. The company said the benefit held across subgroups, including patients with brain or liver metastases.

The cost side

The benefit comes with more toxicity. Cytokine release syndrome, an immune reaction common with this type of drug, occurred in 49.6% of patients who received Imdelltra, almost all of it mild or moderate (41.8% grade 1, 7.4% grade 2, one grade 3 case). Serious neurological events were rare: ICANS occurred in 1.1% and none reached grade 3. The trial also required monitoring in a healthcare setting for 1 to 2 hours after the first two doses, or 6 to 8 hours in some regions including Europe. Amgen has also announced an FDA-approved label update that shortens the monitoring time for those first two doses.

The number behind the number

Imdelltra is currently sold only for patients whose cancer has already progressed after chemotherapy. In its second-quarter results, Amgen reported Imdelltra sales of $288 million, up from $134 million a year earlier, with $233 million in the US and $55 million elsewhere. Against total second-quarter revenue of $10.1 billion, that is under 3%. Multiplied by four, the quarter implies roughly $1.15 billion a year. That is our arithmetic, not a company forecast.

The new trial is aimed at the maintenance phase right after first-line chemotherapy, which every newly diagnosed patient reaches if the disease has not progressed. Amgen's September 8 topline release noted that many patients relapse quickly and "never reach second-line treatment," and that only about 40% receive second-line therapy. A drug used only after progression therefore reaches a minority of patients, and a first-line maintenance drug would reach most of them. What that is worth depends on approval, the label and how long patients stay on treatment, none of which Amgen has disclosed.

The company also cited longer follow-up from an earlier, smaller study, DeLLphi-303, with median survival of 37.9 months from the start of first-line maintenance. That was a Phase 1b trial without a comparison arm, and the upper end of its confidence interval was not estimable, so it is encouraging but not proof.

What to watch

• Regulators. Amgen said it is moving "with urgency" to share the results with regulators worldwide. It gave no filing or decision date.
• Maturing data. This was an interim analysis. The survival curves and any change in the hazard ratio as follow-up lengthens will be scrutinized.
• Safety in a wider group. First-line patients are generally healthier than those treated after progression, but the side-effect rates above will matter for community oncology practices that must run the monitoring.
• Competition. Amgen's release does not discuss rival DLL3-targeted treatments. We did not review competitor data for this story.

Amgen is one of the 30 Dow Jones Industrial Average stocks. For earlier Amgen coverage, see our report on its Sjögren's drug trial, or follow Stocks.

Sources: Amgen press releases via PR Newswire (Oct. 24, Sept. 8 and Aug. 4, 2026); Reuters; Nasdaq and Yahoo Finance price data. All trial results are Amgen's own reported figures; we have not independently reviewed the New England Journal of Medicine paper. This is market information, not investment advice or medical advice.