Full first-line data for Imdelltra arrived on a Saturday. The day Amgen announced the trial had worked, in September, its shares had their worst day in more than two decades, on news about a different drug.
Amgen told investors in September that its lung-cancer drug Imdelltra had extended survival in a large first-line trial. It did not say by how much. Now it has, and the market gets its first chance to respond on Monday.
At the European Society for Medical Oncology congress on Saturday, Amgen and AstraZeneca released interim results from the Phase 3 DeLLphi-305 trial, published simultaneously in the New England Journal of Medicine. Imdelltra, given with AstraZeneca's Imfinzi as maintenance therapy in extensive-stage small cell lung cancer, reduced the risk of death by 58% compared with Imfinzi alone, a hazard ratio of 0.42.
Patients on the combination lived a median of 21.1 months, against 12.7 months for Imfinzi alone, at a median follow-up of about 16 months. Nearly 80% were alive after one year, compared with 53%. Progression-free survival improved with a hazard ratio of 0.34, to a median of 7.4 months from 1.9 months, and 26.4% of patients responded to treatment, against 4.1%.
Amgen called the result "unprecedented." AstraZeneca said the median survival was the longest ever reported in a Phase 3 trial in this setting.
The day the stock fell for another reason
When Amgen announced on Sept. 8 that the trial had met its survival goal, its shares fell 10.1% to $393.17, their largest one-day decline since October 2000. Reporting at the time tied the drop to the failure of a Novartis heart drug, which raised doubts about a similar Amgen program, and to an analyst downgrade.
Since then the stock has recovered 11.7%, closing Friday at $439.26, close to its 52-week high of $450.98. What drove that recovery is not clear. What is clear is that the magnitude of the Imdelltra result was not public until Saturday.
The fine print
The trial enrolled 563 patients whose disease had not progressed after initial treatment with Imfinzi and chemotherapy. It was open-label, meaning patients and doctors knew which treatment was being given, and the results come from a planned interim analysis. Patients in the control arm stayed on treatment for a median of 8.1 weeks, compared with 46.9 weeks on the combination.
Side effects were manageable by the standards of the drug class. Grade 3 or higher treatment-related adverse events occurred in 20.9% of Imdelltra patients versus 10.8% on Imfinzi alone. Cytokine release syndrome, an immune reaction, affected about half of patients but was mostly grade 1, with a single grade 3 case, and treatment discontinuations for side effects were similar in both arms, at 5.7% and 5.8%.
At an investor event on Saturday, Amgen said it is "working to rapidly file," according to a transcript of the event, the data with regulators worldwide. It did not give a date. More than 18,000 patients have been treated with Imdelltra since launch, and it is approved in more than 15 markets.
Big result, modest drug
The case that the numbers matter is straightforward. The trial moves Imdelltra into first-line maintenance, where patients stay on therapy far longer. The competing maintenance regimen, Jazz Pharmaceuticals' Zepzelca with Tecentriq, reduced the risk of death by 27% in its own trial, though comparisons across trials are imprecise.
The case for restraint is scale. Imdelltra sold $288 million in the second quarter, about 2.9% of Amgen's roughly $10.1 billion in quarterly revenue. Analysts expect annual sales above $2.5 billion by 2030, according to LSEG data, which would equal about 7% of Amgen's 2025 revenue. The drug lists at about $390,000 a year, and competitors including Zai Lab, AbbVie, Merck, Novartis and Roche are developing drugs against the same DLL3 target.
What to watch
Monday's move in Amgen shares against biotech benchmarks, the timing of the regulatory submission, longer follow-up from DeLLphi-305 and results from related trials, and Amgen's third-quarter report.