Tarlatamab (Imdelltra) for small cell lung cancer

Small cell lung cancer had one of the worst records for drug development of any solid tumor. After decades during which carboplatin plus etoposide remained the backbone of first-line therapy with little modification, a series of checkpoint inhibitor trials in the late 2010s produced incremental survival benefits, but median overall survival for extensive-stage disease at first line still measured in the range of 12 months. Second-line and beyond was worse: topotecan, the historical standard, yielded response rates below 25% and median survival of roughly six months. The door was wide open for a new approach.

DLL3, a Notch pathway ligand expressed on the surface of the vast majority of SCLC cells but minimally on normal tissue, had been pursued as a target for years. Rovalpituzumab tesirine, an antibody-drug conjugate against DLL3, reached phase 3 and failed, its development halted by toxicity. Amgen and other groups then explored a bispecific format, using the same DLL3 target but engaging CD3 on T cells to direct cytotoxic killing rather than delivering a toxic payload. Tarlatamab was the result. Luis Paz-Ares of the Hospital Universitario 12 de Octubre in Madrid led the registration DeLLphi-301 trial; Melissa Johnson of the Sarah Cannon Research Institute was a co-investigator.

DeLLphi-301 was a single-arm trial; the efficacy population for the approved 10 mg dose comprised 99 patients with extensive-stage SCLC who had received at least two prior lines of therapy. The objective response rate was 40%, and the median duration of response was 9.7 months. Those figures, in a population with historical response rates to third-line therapy well below 20%, were sufficient for the FDA to grant accelerated approval in May 2024 under the brand name Imdelltra. The indication covered SCLC after platinum-based chemotherapy, which in practice meant the majority of relapsed patients.

The bispecific mechanism introduced a distinct toxicity profile. Cytokine release syndrome occurred in a substantial proportion of patients and required the first dose to be given in a monitored inpatient or extended observation setting. Neurologic immune effects, including immune effector cell-associated neurotoxicity syndrome, were also reported. Managing these toxicities required oncology centers to develop protocols similar to those used for CAR-T therapy, which had not previously been part of the standard SCLC workflow.

A subsequent randomized phase 3 trial, DeLLphi-304, compared tarlatamab head-to-head with investigator's choice chemotherapy as second-line therapy. The trial showed median overall survival of 13.6 months with tarlatamab versus 8.3 months with chemotherapy. That result supported converting the accelerated approval to full approval and, if confirmed by regulatory review, would establish tarlatamab as the preferred second-line standard for extensive-stage SCLC, displacing chemotherapy from a position it had held for decades.