Imfinzi Plus Imdelltra Shows Interim Survival Benefit in Extensive-Stage SCLC

AstraZeneca and Amgen reported positive topline results from the planned interim analysis of DeLLphi-305, a Phase III trial of Imfinzi (durvalumab) plus Imdelltra (tarlatamab) as first-line maintenance therapy for extensive-stage small cell lung cancer (ES-SCLC). The combination produced a statistically significant and “highly clinically meaningful” improvement in overall survival compared with Imfinzi alone. 7

The announcement is potentially important for a cancer in which treatment options remain limited. But it is not yet a complete clinical-data readout: the companies have not disclosed the magnitude of the survival benefit, detailed response results, or the full safety dataset. 67

What DeLLphi-305 found

At the prespecified interim analysis, the Imfinzi–Imdelltra combination met the trial’s primary endpoint of overall survival. It also showed statistically significant improvements in progression-free survival and objective response rate versus Imfinzi alone. 67

AstraZeneca and Amgen described the survival result as highly clinically meaningful. That language reflects the companies’ topline assessment; until a medical-meeting presentation or peer-reviewed publication provides the underlying hazard ratios, medians, confidence intervals, and adverse-event rates, the practical size of the benefit cannot be independently assessed. 67

Who was studied and how the trial worked

DeLLphi-305 enrolled 563 patients with ES-SCLC who had not progressed after induction treatment with Imfinzi plus platinum chemotherapy and etoposide. Participants were randomly assigned 1:1 to receive durvalumab plus tarlatamab or durvalumab alone, continuing treatment until disease progression or unacceptable toxicity. 710

This is a maintenance strategy: it tests whether adding tarlatamab after successful initial chemo-immunotherapy can extend disease control and survival, rather than reserving the drug for cancer that has already relapsed.

Why the combination could matter

Tarlatamab is a DLL3-directed, CD3 T-cell engager. It is designed to bind DLL3 on tumor cells and CD3 on T cells, bringing T cells into contact with DLL3-expressing cancer cells and promoting T-cell-mediated killing. 7

AstraZeneca characterized DeLLphi-305 as the first demonstrated survival benefit from combining an immune-checkpoint inhibitor with a DLL3×CD3 bispecific T-cell engager in this setting. 7 The result therefore tests a distinct clinical concept: combining ongoing PD-L1 inhibition from durvalumab with a therapy intended to redirect T cells toward a tumor-associated target.

Safety and what is still unknown

The companies said the combination’s safety profile was consistent with the known profiles of the individual medicines and that no new safety signals were identified. 67

That is encouraging but incomplete. Detailed safety reporting will be especially important because treatment decisions depend on the frequency, severity, and management of adverse events—not only on a topline statement that no new signal emerged.

AstraZeneca and Amgen said they plan to present the complete results at a future medical meeting and submit them to regulators. Until then, Imfinzi plus Imdelltra remains an investigational frontline-maintenance approach. 7

How this could change Imdelltra’s role

Imdelltra’s established development story has been in previously treated SCLC. In the Phase III DeLLphi-304 trial, Amgen reported that tarlatamab reduced the risk of death by 40% versus standard chemotherapy in patients whose SCLC had progressed on or after platinum-based chemotherapy; reported median overall survival was 13.6 months with tarlatamab versus 8.3 months with chemotherapy. 15

DeLLphi-305 points to a possible earlier use: maintenance immediately after patients complete non-progressive Imfinzi-based induction. If the full results support the interim analysis and regulators authorize this use, clinicians could have a tarlatamab-based option before relapse rather than only after platinum-based treatment has failed. That outcome is not assured, however, and should not be assumed until the complete evidence and regulatory decisions are available.

Bottom line

The DeLLphi-305 interim analysis gives AstraZeneca and Amgen a positive Phase III survival result for Imfinzi plus Imdelltra in first-line maintenance treatment of ES-SCLC. The trial also met progression-free-survival and response-rate endpoints, while the companies reported no new safety signals. 67

For now, the key limitation is the absence of detailed data. The upcoming full presentation will determine how large the benefit is, which patients benefited most, and whether the risk–benefit profile supports a new frontline-maintenance option.