Phase 3 Trial Shows Adding Imdelltra to First-Line Treatment Helps Patients With SCLC Live Longer

For people with extensive-stage small cell lung cancer (ES-SCLC), the first round of treatment often works, but the cancer usually returns quickly. Many people never become well enough for a second treatment. That's why a new result is drawing attention.

On Sept. 8, 2026, Amgen announced that its phase 3 DeLLphi-305 trial met its main goal: adding Imdelltra (tarlatamab) to Imfinzi (durvalumab) as maintenance therapy after first-line treatment helped people live longer than Imfinzi alone.

Why Maintenance Treatment Matters

For people with ES-SCLC, initial treatment typically includes immunotherapy combined with chemotherapy. While this approach can shrink tumors and control the disease, SCLC can be aggressive and often begins growing again after the initial treatment.

Maintenance therapy is given after the cancer has responded to or remained stable following initial treatment. The goal is to keep the cancer under control for as long as possible and delay progression.

Imdelltra is a bispecific T-cell engager, meaning it is designed to help the body's immune system recognize and attack cancer cells. It targets DLL3, a protein commonly found on SCLC cells, while also engaging T cells to help destroy those cancer cells.

Who Was in the Trial

DeLLphi-305 enrolled 563 people with ES-SCLC whose cancer had not grown after initial treatment with Imfinzi plus platinum chemotherapy and etoposide. They were randomly assigned to continue Imfinzi alone or to receive Imfinzi plus Imdelltra.

Researchers were primarily looking at overall survival, which measures how long people live after entering the trial. They also looked at progression-free survival, which measures how long people live without their cancer getting worse, as well as tumor response.

What the Trial Found

At a planned interim analysis, the combination significantly improved overall survival, the trial's main goal, compared with Imfinzi alone. The combination also improved progression-free survival and the proportion of patients whose tumors shrank.

Importantly, Amgen reported that no new safety concerns were identified with the combination. However, the companies have not yet released the specific survival numbers from the trial. Full results are expected to be presented at an upcoming medical meeting, where researchers will provide more details about how much longer people lived and how long their cancer remained controlled.

The findings are notable because DeLLphi-305 is the first phase 3 trial to show that a bispecific T-cell engager can improve survival when used as part of first-line maintenance treatment for SCLC.

Imdelltra is already being studied and used in other SCLC treatment settings, but it is not currently approved for this particular first-line maintenance use. The new findings could potentially support a future regulatory submission for this treatment approach.

Another SCLC Drug Hits a Setback

While the DeLLphi-305 results offer encouraging news, another recent development highlights how difficult it can be to bring new SCLC treatments to patients.

In late September, Daiichi Sankyo and Merck voluntarily withdrew their application for accelerated approval of ifinatamab deruxtecan in previously treated ES-SCLC after discussions with the FDA found that data from a phase 2 trial were not sufficient to support the application. Studies of the drug continue, and researchers are still evaluating its potential role in SCLC.

Together, these developments highlight the ongoing effort to find treatments that can keep SCLC under control for longer and give patients more options when the disease returns.

What This Could Mean for Patients

The DeLLphi-305 results do not mean that Imdelltra is currently a standard maintenance treatment for everyone with ES-SCLC. More detailed trial results and regulatory decisions will be needed before doctors know how the findings may change routine treatment.

For patients whose cancer has responded to first-line treatment, however, the study raises an important question: Could adding a targeted immune-based treatment help keep the cancer from returning or growing for longer?

Questions to Ask Your Care Team

• Is Imdelltra an option for me now, or should I consider a clinical trial?
• If this combination is approved, would I be a candidate after my first treatment?
• What are the potential benefits and side effects of adding Imdelltra to maintenance therapy?
• Are there clinical trials for extensive-stage small cell lung cancer that I may qualify for?

References

1. AstraZeneca. "Imfinzi (Durvalumab) Plus Tarlatamab Demonstrated a Statistically Significant and Highly Clinically Meaningful Improvement in Overall Survival and Progression-Free Survival in 1st-Line Extensive-Stage Small Cell Lung Cancer." Business Wire, Sept. 8, 2026.
2. Pharmacy Times. "Tarlatamab Plus Durvalumab Improves Survival in First-Line ES-SCLC." Sept. 9, 2026.
3. OncLive. "Ifinatamab Deruxtecan BLA Voluntarily Withdrawn in Previously Treated Extensive-Stage SCLC." Sept. 25, 2026.