| Subtype | Transcription factor / defining program | Approx. frequency | Neuroendocrine status | Key molecular features / pathway enrichment | Suggested targeted therapies / vulnerabilities |
|---|---|---:|---|---|---|
| SCLC-A | **ASCL1** | ~70% | NE-high | Canonical neuroendocrine subtype; enriched for **BCL2, DLL3, SOX2, RET, MYCL1** and ASCL1-driven lineage programs (pqac-00000004, pqac-00000006, pqac-00000008, pqac-00000031) | **DLL3-targeting agents** (e.g., tarlatamab), **BCL2 inhibitors** (venetoclax), **LSD1 inhibitors**, **HDAC inhibitors**; RET/BCL2-directed strategies under study (pqac-00000006, pqac-00000014) |
| SCLC-N | **NEUROD1** | ~15% | NE-high | More aggressive/proliferative state; associated with **MYC co-expression/amplification**, neuronal signaling, chemoresistance, and elevated **AURKA/AURKB** dependence (pqac-00000004, pqac-00000006, pqac-00000008, pqac-00000031) | **Aurora kinase inhibitors** (e.g., alisertib), MYC-directed approaches, cell-cycle pathway targeting; IMPDH inhibitors proposed in review literature (pqac-00000006, pqac-00000031) |
| SCLC-P | **POU2F3** | 7–15% | NE-low / non-NE | Tuft-cell-like subtype; depends on **IGF1R signaling** and shows relative **DNA repair deficiencies**; transcriptomically distinct from classic NE SCLC (pqac-00000004, pqac-00000008, pqac-00000028, pqac-00000031) | **IGF1R inhibitors**, **PARP inhibitors**, DNA-damaging agents, SWI/SNF ATPase-directed approaches proposed for selected tumors (pqac-00000006, pqac-00000031) |
| SCLC-Y | **YAP1** (debated as stable subtype in some studies) | 3–10% | NE-low / non-NE | Linked to low-NE state, lineage plasticity, EMT/non-NE features, and therapy resistance; YAP/Notch/REST programs implicated. Some reviews note this category is biologically less stable or inconsistently reproduced across datasets (pqac-00000004, pqac-00000008, pqac-00000026, pqac-00000029) | No single standard targeted therapy; candidate approaches include **ERBB pathway targeting** in specific low-NE/YAP-associated transitions and broader plasticity-directed/epigenetic strategies (pqac-00000007, pqac-00000025, pqac-00000029) |
| SCLC-I | **Inflamed / immune program** rather than dominant ASCL1/NEUROD1/POU2F3 | Not firmly fixed; distinct subset | Often NE-low / inflamed | Characterized by **inflamed gene signatures**, higher **HLA/antigen-presentation**, immune checkpoint expression, mesenchymal features, and greater immune-cell infiltration versus NE-high “immune desert” tumors (pqac-00000003, pqac-00000021, pqac-00000030) | Greatest rationale for **immune checkpoint blockade**; biomarker-enriched immunotherapy strategies and combination immunotherapy approaches are emphasized (pqac-00000003, pqac-00000017, pqac-00000030) |


*Table: This table summarizes the main molecular subtypes of small cell lung cancer, their defining transcriptional programs, approximate frequencies, biologic features, and leading therapeutic hypotheses. It is useful for mapping subtype biology to emerging precision-treatment strategies.*