Amgen's Imdelltra Plus Imfinzi Cuts Risk of Death 58% in Phase 3 Small Cell Lung Cancer Trial

Adding Amgen's Imdelltra to AstraZeneca's Imfinzi cut the risk of death by 58% in patients with extensive-stage small cell lung cancer, according to full Phase 3 results released Saturday, Oct. 24.

The DeLLphi-305 data were presented in the Presidential Symposium at the European Society for Medical Oncology Congress in Madrid and published simultaneously in the New England Journal of Medicine.

What the trial found

The study enrolled 563 patients at 175 centers in 29 countries. All had extensive-stage disease, meaning the cancer had spread beyond the lung, and all had responded to first-line Imfinzi plus chemotherapy without progressing.

They were randomized to maintenance treatment with Imdelltra (tarlatamab) plus Imfinzi (durvalumab), or Imfinzi alone.

Median overall survival was 21.1 months with the combination versus 12.7 months with Imfinzi alone, a gain of 8.4 months. Median progression-free survival was 7.4 months versus 1.9 months, a 66% lower risk of progression or death.

Dr. Jacob Sands of Dana-Farber's Lowe Center for Thoracic Oncology, the lead investigator, said the benefit showed up across subgroups, including patients whose cancer had spread to the brain or liver. Those patients usually do worse.

Small cell lung cancer is brutal. Chemotherapy often works at first, then the disease returns within months. About 31,000 Americans are diagnosed each year, and an estimated 60% to 70% of them have extensive-stage disease.

The caveats

The 58% figure is a relative reduction in the risk of death during the study. It is not an absolute drop in mortality.

This is also an interim analysis, with roughly 16 months of median follow-up. Sands said the 21-month figure "may evolve further and hopefully will substantially improve," as it did in Amgen's earlier Phase 1 work.

There is a cost in side effects. Grade 3 or higher treatment-related adverse events hit 20.9% of patients on the combination, versus 10.8% on Imfinzi alone. About half of the combination patients had cytokine release syndrome, nearly all of it mild. There was one grade 3 case.

What the people involved are saying

Amgen Chief Medical Officer Dr. Paul Burton did not hold back. "I think there are moments in medicine when you see a piece of data that is so profound that it's going to transform the standard of care for patients, and I think, honestly, we're at that moment," he said. He added that the combination could "almost convert" one of the most aggressive cancers "into a chronic disease." Burton is the company's own executive, and he is describing the company's own drug.

Outside oncologists were also enthusiastic. Prof. Ido Wolf, head of oncology at Tel Aviv Sourasky Medical Center, wrote on X after the presentation that the audience was "absolutely ecstatic" and called a median survival beyond 21 months "an extraordinary figure for this disease." Israeli media reported the presentation drew a standing ovation.

The business angle

Imdelltra posted $288 million in second-quarter sales, up 115% from a year earlier, after $627 million in global sales in 2025. Burton said the drug's current label covers about 13,000 U.S. patients. That could rise to 35,000 to 40,000 if Amgen's earlier-line trials also succeed.

Amgen announced on Sept. 8 that DeLLphi-305 had met its survival goal but held the numbers for ESMO. The stock has not traded on the full data. According to a TIKR analysis, Amgen shares closed at a record $447.28 on Oct. 22, up more than a third this year.

That analysis argues the news may already be in the price. It notes Imdelltra is about 2.9% of the $10.05 billion Amgen booked last quarter. Prolia and Xgeva sales fell from a combined $1.65 billion to $1.11 billion over the past year as biosimilars arrived, a $540 million drop, nearly twice Imdelltra's whole quarter. TIKR also points out that Amgen trades at 18.62 times forward normalized earnings, near its one-year high of 18.96.

Amgen raised its 2026 revenue guidance to between $38.2 billion and $39.4 billion after beating estimates in the second quarter.

What comes next

U.S. markets reopen Monday, Oct. 26, the first session since the full numbers became public.

The clinical question is how the survival curves hold up with longer follow-up. The commercial one is whether Amgen's earlier-line trials in small cell lung cancer deliver the results Burton says would nearly triple the eligible U.S. patient pool.