Limitations of Phase 1B Data and Biomarker Development in ES-SCLC

Dr. Shields addresses limitations of phase 1b single-arm studies, noting smaller patient numbers may introduce selection bias toward patients most likely to benefit from T-cell engager therapy targeting DLL3 and CD3. She emphasizes the importance of randomized phase 3 data for head-to-head comparisons, particularly given that DeLLphi-303's control arm involved immunotherapy alone, preventing cross-trial comparisons with IMforte's different control arm.

Dr. Leal discusses differentiating positive DeLLphi-305 results from IMforte data, emphasizing that beyond OS, CNS-specific endpoints prove crucial. ASCO 2026 data showed DeLLphi-304 demonstrated improved CNS PFS compared to chemotherapy, with 15% CNS response rates including complete responses. This CNS activity becomes particularly relevant for frontline maintenance patients at risk for baseline or progressive brain metastases.

Regarding PD-L1 inhibitor interchangeability, Dr. Sands notes DeLLphi-303 paired tarlatamab with either atezolizumab or durvalumab showing similar benefit, though acknowledges this represents early phase data. He's hopeful that biomarker-driven approaches will eventually differentiate SCLC subtypes for personalized treatment selection.

Dr. Chiang describes the ongoing SWOG S1827/PRISM trial collecting tissue from 800 patients during induction to identify molecular subtypes, randomizing patients to biomarker-directed therapy plus immunotherapy versus immunotherapy alone, representing important groundwork for future precision medicine approaches, though not yet ready for clinical implementation. Dr. Shields confirms biomarkers remain in development requiring further validation before guiding treatment selection.