After a decade in which small-cell lung cancer absorbed one failed cytotoxic after another, antibody-drug conjugates have created a real therapeutic conversation in this disease — three platforms (DLL3, B7-H3, SEZ6) with phase-2 activity that warrants moving toward phase-3 confirmation.
01 · RationaleWhy ADCs, and Why Now
SCLC is biologically dominated by lineage transcription factors (ASCL1, NEUROD1, POU2F3, YAP1). Surface proteins enriched on these lineages — DLL3, B7-H3, SEZ6 — give us drug-deliverable targets that monoclonal antibodies alone cannot meaningfully exploit. ADCs combine that addressing with payload chemistry (topoisomerase-1 inhibitors, MMAE-class tubulin disruptors) potent enough to matter in a disease that doubles in days.
02 · DLL3DLL3: From Rovalpituzumab to Tarlatamab and Beyond
The DLL3 story is well-known and instructive. Rovalpituzumab tesirine failed in two phase-3 trials largely on toxicity; the target was vindicated by tarlatamab (BiTE), and a new DLL3 ADC generation with cleaner linker-payload combinations is now back in early-phase testing.
The lesson from rovalpituzumab is that target expression matters less than payload manageability. We’ve spent five years re-learning that.
— Charles Rudin, MD · ILCS 2025 chair address
03 · B7-H3B7-H3 ADCs: Ifinatamab and the Topo-I Era
Ifinatamab deruxtecan (I-DXd) has the most mature SCLC dataset for a B7-H3-directed ADC, with phase-2 response rates in the 30–40% range in heavily pretreated patients. Crucially, activity is largely independent of baseline B7-H3 IHC scoring above a low expression floor — consistent with the bystander effect of the deruxtecan payload class.
03.1Open Biomarker Questions
If response decouples from target IHC, what selects the right patient? Early signal suggests transcriptomic subtypes (NEUROD1-high) and circulating tumour DNA clearance kinetics may matter more than IHC, but neither is ready for routine clinical use.
Key takeaways
Where the SCLC ADC field stands
- Three classes (DLL3, B7-H3, SEZ6) have credible phase-2 SCLC activity; phase-3 confirmation is the next inflection.
- Target IHC is not yet a reliable biomarker for ADC response — the payload’s bystander effect uncouples surface expression from activity.
- Pneumonitis (deruxtecan class) and infusion reactions (BiTE-adjacent platforms) define the practical safety frontier.
- Combination with immunotherapy is the obvious next combinatorial question; early signals are cautiously encouraging.
ReferencesSelected Reading
- Rudin CM et al. The molecular landscape of small-cell lung cancer: lineage subtypes and therapeutic implications. Nat Rev Cancer. 2024.
- Johnson ML et al. Ifinatamab deruxtecan in previously treated extensive-stage SCLC. J Thorac Oncol. 2025.
- Aggarwal C et al. Emerging SEZ6-targeted ADCs in SCLC: early-phase activity. Cancer Discov. 2025.
