Adding tarlatamab (Imdelltra) to durvalumab (Imfinzi) helped people with extensive-stage small cell lung cancer live longer than durvalumab alone, according to results from the phase 3 DeLLphi-305 trial presented at the 2026 European Society for Medical Oncology Congress in Madrid. The combination was given as maintenance treatment—ongoing therapy after initial treatment to help keep cancer under control.
Median overall survival was 21.1 months with the combination, compared with 12.7 months with durvalumab alone—an improvement of more than eight months. At one year, approximately 79% of patients receiving the combination were alive, compared with 53% receiving durvalumab alone.investors.
Who took part in the study?
The trial enrolled 563 people with extensive-stage small cell lung cancer whose cancer had not worsened after initial treatment with durvalumab, platinum-based chemotherapy and etoposide. Participants were randomly assigned to receive either tarlatamab plus durvalumab or durvalumab alone.investors.
This distinction matters: the study tested adding tarlatamab after initial chemotherapy and immunotherapy, not replacing those initial treatments. The findings apply to patients whose cancer remained controlled when they entered the maintenance phase.
Longer survival and more time before cancer worsened
In addition to extending survival, the combination delayed cancer progression. Median progression-free survival—the time before cancer worsened or a patient died—was 7.4 months with tarlatamab plus durvalumab, compared with 1.9 months with durvalumab alone.
The combination reduced the risk of death during the study by 58% and the risk of progression or death by 66%. These figures describe differences between the treatment groups over follow-up; they do not predict an individual patient’s outcome. Likewise, median survival is the midpoint of study results, not a limit on how long someone can live.investors.
Researchers reported survival benefits across several patient subgroups, including those with cancer that had spread to the brain or liver.
How does the combination work?
Tarlatamab is a type of immunotherapy called a bispecific T-cell engager. It helps bring cancer-fighting immune cells called T cells into contact with small cell lung cancer cells. Durvalumab is another form of immunotherapy. The study tested whether combining these approaches during maintenance treatment could improve on durvalumab alone.
What were the side effects?
Treatment-related side effects were more common with the combination. Severe treatment-related side effects occurred in approximately 21% of patients receiving tarlatamab plus durvalumab, compared with 11% receiving durvalumab alone. Reported side effects included low neutrophil counts—a type of white blood cell—as well as decreased appetite, fatigue and weight loss.
About half of patients receiving the combination experienced cytokine release syndrome, an inflammatory reaction associated with treatments that activate T cells. Most cases were mild or moderate and resolved with supportive care. Severe cases occurred in fewer than 1% of patients.
Although treatment-related side effects were more frequent, a similar proportion of patients in each group stopped treatment because of them.
What do the results mean for patients?
The findings provide strong evidence that adding tarlatamab during maintenance treatment can improve survival for people with extensive-stage small cell lung cancer whose disease has not progressed after initial chemoimmunotherapy. However, these are interim results, and continued follow-up will help clarify longer-term outcomes.
For patients approaching maintenance treatment, the results offer a specific topic to discuss with their oncology team: whether this approach is appropriate and available for their situation, and how its potential benefits compare with the additional side effects and monitoring it requires. The trial does not answer whether the combination offers the same benefit when cancer has already progressed during initial treatment.
Reference
Sands J, Yoshida T, Ahn MJ, et al. Tarlatamab plus durvalumab vs durvalumab as first-line maintenance therapy following first-line durvalumab, platinum, and etoposide in extensive-stage small cell lung cancer: primary analysis of the phase 3 DeLLphi-305 trial. Presented at: European Society for Medical Oncology (ESMO) Congress 2026; October 23–27, 2026; Madrid, Spain. Abstract LBA3.
