Instead of replicating the ADC and checkpoint inhibitor combination successful in other cancers, experts suggest a more "sophisticated" approach for prostate cancer. The next step should be combining ADCs with T-cell engagers, which have shown greater single-agent efficacy in this specific disease, potentially leapfrogging a less effective strategy.

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.

The novel target DLL3 is a promising avenue for treating NECs, but its therapeutic efficacy is highly dependent on expression levels. Early trial data for a DLL3 T-cell engager showed a 40% response rate in high-expressing tumors versus just 3% in low-expressors, mandating biomarker testing for patient selection.

After standard immunotherapy biomarkers like PD-L1 and TMB proved ineffective in SCLC, the field shifted to a more direct approach. Novel therapies like the bispecific antibody tarlatumab target surface proteins such as DLL3, physically bridging immune cells to cancer cells without relying on predictive biomarkers.

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.

Despite widespread use in oncology, immunotherapy has limited efficacy in extrapulmonary NEC. Real-world data for combination CTLA-4 and PD-1 inhibitors show response rates around 15%, with sustained responses in less than 10% of patients. This highlights the urgent need for novel therapeutic approaches beyond checkpoint inhibition.

Contrary to common belief, HER2 can be expressed or amplified in prostate cancer, particularly in subtypes with neuroendocrine features. This creates a rare but actionable target, with reported complete responses to HER2-directed therapies like TDXD, highlighting the need for broader genomic 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.

To combat immunosuppressive "cold" tumors, new trispecific antibodies are emerging. Unlike standard T-cell engagers that only provide the primary CD3 activation signal, these drugs also deliver the crucial co-stimulatory signal (e.g., via CD28), ensuring full T-cell activation in microenvironments where this second signal is naturally absent.