Tarlatamab plus durvalumab cuts death risk 58% in extensive stage small cell lung cancer

Extensive stage small cell lung cancer has long been one of the hardest diagnoses in oncology. It accounts for roughly 13% to 15% of lung cancer cases, grows rapidly, and has a five year survival rate across all stages of about 9% according to the American Cancer Society. For years, first line treatment has relied on platinum chemotherapy plus etoposide, with immunotherapy added more recently. Even with that progress, most patients see their disease return quickly, and median survival after first line maintenance has remained short.

The DeLLphi-305 trial tested whether moving tarlatamab (Imdelltra) earlier, into first line maintenance, could change that trajectory. Tarlatamab is a bispecific antibody: one arm binds CD3 on T cells, the other binds DLL3, a protein found on most small cell lung cancer cells, bringing the immune cell and the tumour cell together. It is already approved in the European Union and the United Kingdom for relapsed small cell lung cancer, and in the United States for patients whose disease progressed during or after platinum based chemotherapy. DeLLphi-305 asked what happens when the drug is used straight after initial chemoimmunotherapy, before progression.

Amgen announced on October 24, 2026 that the phase 3 trial had produced a 58% reduction in the risk of death when tarlatamab was added to AstraZeneca's durvalumab (Imfinzi) maintenance. The results were presented in Presidential Symposium I at the ESMO Congress 2026 in Madrid as abstract LBA3 and published simultaneously in The New England Journal of Medicine. The headline numbers were median overall survival of 21.1 months for the combination versus 12.7 months for durvalumab alone, with a hazard ratio of 0.42 (95% CI 0.32 to 0.54; P less than 0.001) at a median follow up of approximately 16 months. The figures drew a standing ovation in Madrid, according to Ynetnews, and specialists described the result as a potential turning point.

Key Facts

DeLLphi-305 (NCT06211036) enrolled 563 adults with extensive stage small cell lung cancer and ECOG performance status 0 to 1 whose disease had not progressed after four cycles of induction platinum and etoposide plus durvalumab. Patients with asymptomatic untreated or treated brain metastases were eligible. The trial randomised patients 1:1 to tarlatamab 10 mg every two weeks plus durvalumab 1500 mg every four weeks, or durvalumab 1500 mg every four weeks, until progression or unacceptable toxicity. Randomisation was stratified by brain and/or liver metastases, response to induction chemoimmunotherapy and prior platinum. The international trial treated patients at 175 medical centres across 29 countries, with 282 people assigned to the combination and 281 to durvalumab alone. AstraZeneca supplied durvalumab and partially funded the Amgen sponsored study.

At the prespecified interim analysis, median overall survival was 21.1 months (95% CI 20.8 to not estimable) with the combination versus 12.7 months (95% CI 11.2 to 14.8) with durvalumab alone. The hazard ratio for death was 0.42 (95% CI 0.32 to 0.54; P less than 0.001), a 58% relative reduction in the risk of death. Nearly 80% of patients on the combination, 79.4%, were alive at one year versus 53.3% on durvalumab alone. Ynetnews reported on October 24, 2026 that 87 patients in the combination group had died versus 156 in the control group.

Progression free survival was 7.4 months (95% CI 5.6 to 9.1) versus 1.9 months (95% CI 1.9 to 2.0), with a hazard ratio of 0.34 (95% CI 0.28 to 0.42; P less than 0.001), a 66% reduction in the risk of disease progression or death. Twelve month progression free survival was 38% versus 10%. Confirmed objective response was 26.4% versus 4.1%, more than six times higher, and median duration of response was 12.7 months versus 5.6 months. At the data cutoff of July 7, 2026, 43.6% of combination patients remained on treatment versus 11.4% on durvalumab alone.

Safety was consistent with the known profile of each drug, but the combination added burden. Grade 3 or higher treatment related adverse events occurred in 20.9% of combination patients versus 10.8% on durvalumab alone. Cytokine release syndrome occurred in 49.6% of patients receiving tarlatamab versus 1.4% on durvalumab alone, predominantly grade 1 (41.8%) or grade 2 (7.4%), with one grade 3 event (0.4%) and none grade 4 or higher. ICANS occurred in 1.1% with no grade 3 or higher events and no deaths from either side effect. Patients were monitored in a healthcare setting for one to two hours after infusion on Cycle 1 Day 1 and Day 8, or six to eight hours in some regions including Europe. OncLive reported on October 24, 2026 that the interim analysis was triggered at 243 deaths, a 61% information fraction. The hazard ratio for death favoured the combination in patients with brain metastases (n=111; HR 0.49; 95% CI 0.26 to 0.93), liver metastases (n=183; HR 0.41; 95% CI 0.28 to 0.61) and stable disease after induction (n=64; HR 0.40; 95% CI 0.19 to 0.85). In patients enrolled in the Americas (n=75), the hazard ratio was 0.82 (95% CI 0.39 to 1.71).

Analysis

What this really means is that extensive stage small cell lung cancer may finally have a maintenance strategy that changes the shape of the survival curve, not just the speed of an initial response. The 58% figure is a relative reduction in the risk of death during the study, not an absolute reduction in mortality, as Ynetnews reported on October 24, 2026. The absolute difference in median overall survival was 8.4 months, and the one year survival difference was 26.1 percentage points. In a disease where median survival has been measured in months, that is a meaningful shift. The hazard ratio of 0.42 is unusually low for a Phase III trial in this setting, and the progression free survival hazard ratio of 0.34 reinforces that the benefit begins early. Jay Bradner, Amgen's executive vice president for R&D, called the magnitude of benefit 'rarely seen in this aggressive disease'.

The bigger picture here is that the result is strong but not simple. The benefit was consistent across prespecified subgroups, including patients with brain and liver metastases, which matters because those groups often have poor outcomes. Yet the Americas subgroup, with only 75 patients, had a hazard ratio of 0.82 and a confidence interval that crossed 1. That does not overturn the overall result, but it is a reminder that subgroup analyses are fragile. Lung Cancer Europe explained on October 24, 2026 that DeLLphi-305 did not directly compare the regimen with maintenance lurbinectedin (Zepzelca), so that comparison will come from cross trial analysis. OncLive reported on October 24, 2026 that Jacob Sands of Dana-Farber Cancer Institute, who presented the data, noted that response rate has limited interpretive value in the maintenance setting and that oligoprogression treated with radiation allowed some patients to stay on study therapy.

Business Wire reported on October 24, 2026 that AstraZeneca described the median overall survival of nearly two years as the longest benefit ever reported in extensive stage disease in a Phase III trial. That claim is company framing, but the underlying number is the number that matters. The combination also carries a monitoring burden because of cytokine release syndrome. A 49.6% CRS rate, even if mostly grade 1 or 2, means infusion reactions must be managed in a setting prepared for them. The one to two hour monitoring period after the first two infusions, or six to eight hours in some regions including Europe, affects how and where treatment can be delivered. The updated DeLLphi-303 data, with median follow up of 30.8 months, showed median overall survival of 37.9 months from the start of first line maintenance with tarlatamab plus anti PD L1 therapy, with 58.1% alive at two years. Those are different trials, so they cannot be added together, but they point in the same direction.

Why It Matters

Small cell lung cancer is fast growing and historically difficult to treat. The American Cancer Society estimate of about 9% five year survival across all stages captures the scale of the unmet need. A median overall survival of 21.1 months in the first line maintenance setting is therefore not a marginal improvement. It gives patients and clinicians a new reference point for conversations about prognosis and treatment. It also gives regulators and health technology assessors a clear survival endpoint to weigh, even as they examine side effects, monitoring requirements and cost.

The reaction in Madrid showed how much the field has been waiting for this kind of result. Ynetnews reported on October 24, 2026 that the findings prompted a standing ovation. Prof. Ido Wolf, head of oncology at Tel Aviv Sourasky Medical Center (Ichilov Hospital), wrote on X that the audience was 'absolutely ecstatic' and called the survival gain 'an extraordinary figure for this disease'. He added that the results were even more exciting than recent advances in pancreatic cancer. Enthusiasm is not approval, but it shapes how quickly clinicians ask for access. The benefit in patients with brain metastases is particularly important because those patients are often managed with radiation and have limited systemic options.

Next Up

Amgen said it is moving with urgency to share results with regulators worldwide. The DeLLphi-305 data are conference and journal data, not a regulatory approval. Lung Cancer Europe explained on October 24, 2026 that any change to European standard of care must go through the European Medicines Agency and then national health technology assessment bodies. In the United States, the FDA shortened the labelled monitoring period after the first two doses of tarlatamab to six to eight hours in September 2026, a change that may ease delivery if tarlatamab moves into earlier lines. Further follow up will be needed to confirm the durability of the survival benefit, to clarify the Americas subgroup signal and to compare outcomes with maintenance lurbinectedin through cross trial analysis.

OncLive reported on October 24, 2026 that Jacob Sands of Dana-Farber Cancer Institute said the outcomes support tarlatamab plus durvalumab as a new standard of care first line maintenance therapy in extensive stage small cell lung cancer. Those details will matter as investigators, regulators and payers decide how to translate a landmark survival result into routine practice. The next year of follow up, regulatory review and real world experience will determine whether the Madrid standing ovation becomes a lasting change in care.