SMARCA4 Loss Promotes Late-Stage Tumor Progression in Nonneuroendocrine Small Cell Lung Cancer

The role of SMARCA4, a core component of the SWI/SNF chromatin remodeling complex, remains unclear in small cell lung cancer (SCLC). Using genetically engineered mouse models, we found that SMARCA4 deletion markedly reduced tumor formation and decreased expression of ASCL1, a key neuroendocrine lineage factor. However, SMARCA4-deficient tumors, although smaller, exhibited aggressive features, including variant histology and loss of neuroendocrine differentiation. In established tumor cells, SMARCA4 knockdown did not affect proliferation in vitro but unexpectedly promoted tumor growth in vivo, accompanied by reduced expression and cell surface display of polio virus receptor, a ligand critical for T- and NK-cell activation. Although the contribution of these immune cells to SMARCA4 tumor suppressor activity remains unknown, these findings suggest distinct roles of SMARCA4 in promoting early tumor development but restraining progression of late-stage, neuroendocrine-low tumors. IMPLICATIONS: This study underscores the importance of tumor context and timing in understanding and targeting SMARCA4 and other chromatin regulators in SCLC.