Access to DLL3 testing is a major bottleneck for treating neuroendocrine carcinomas. However, the immunohistochemical stain is described as an extremely easy, 'out of the box' procedure. This suggests the barrier is awareness and institutional priority, not technical complexity, and that pathologists can be pressured to set it up in-house.
Clinical data from a first-in-human trial of the T-cell engager Obrextamic reveals a dramatic efficacy difference based on a key biomarker. Patients with high DLL3 expression had a 40% response rate, producing deep, durable responses. This is in stark contrast to a negligible 3% response rate in the low-DLL3 cohort, cementing the need for expression testing.
Early data from the Darien-7 trial shows combining the DLL3 T-cell engager Obrextamic with first-line chemotherapy achieves a near 75% response rate in EpNEC patients. Critically, it also extends the median duration of response to 8.8 months, more than double the historical average for chemotherapy alone, indicating a synergistic and highly durable effect.
While high DLL3 expression is a key predictor for most T-cell engagers, early data for the tri-specific antibody Gossetamic shows responses in both high and low DLL3 prostate neuroendocrine carcinomas. This suggests the biology of prostate NECs may differ, questioning if DLL3 expression is a universal biomarker for all extrapulmonary neuroendocrine carcinoma subtypes.