Clinical Development of DLL3-Targeted Therapies and Future Directions

Dr. Strosberg discusses tarlatamab, a bispecific T-cell engager targeting DLL3 on tumor cells and CD3 on T-cells, bringing cytotoxic T-lymphocytes into close proximity with cancer cells to induce targeted cell death. Although another DLL3-targeting antibody received approval for SCLC, tarlatamab has focused research efforts on both pulmonary and extrapulmonary NECs, making it particularly relevant for specialists managing rare extrapulmonary disease.

Early Phase 1 data demonstrates promising activity in approximately 60 patients with extrapulmonary NECs. Critical findings reveal clear activity distinction based on DLL3 expression levels: roughly half demonstrated less than 50% DLL3 expression while the remainder showed above 50% expression. High DLL3 expressors achieved approximately 40% response rates with encouraging response durations, whereas low DLL3 groups showed only one responder (3% objective response rate) with poor median PFS.

Current research focuses on high DLL3 expressors, though immunohistochemistry-based cutoffs remain relatively subjective. Staining intensity scores (1+, 2+, 3+) introduce additional subjectivity challenges, though this represents important progress toward personalized treatment approaches. High DLL3 expression appears in approximately half of patients showing any degree of DLL3 positivity, with any DLL3 expression detected in roughly 75% of patients with extrapulmonary NECs.

For patients like James with 85% DLL3 positivity, clinical trial enrollment represents optimal management given lack of effective standard therapies. Multiple DLL3-targeting strategies under development include bispecific T-cell engagers, antibody-drug conjugates, CAR-T cells, and radiopharmaceuticals, all showing promising preclinical and early clinical activity.

Dr. Strosberg anticipates DLL3-targeted treatments becoming standard second-line care in the near future, with eventual first-line integration through combination strategies with chemotherapy. Early-phase trials investigate optimal sequencing including upfront combination, delayed addition after initial cycles, or maintenance approaches following chemotherapy. Given that many patients never reach second-line therapy due to rapid progression and performance status decline, first-line incorporation could benefit significantly more patients with this aggressive malignancy.