Neutrophil extracellular traps-STC1 positive feedback loop promotes immune evasion and metastasis in bladder cancer

Background: Immune checkpoint inhibitors (ICIs) have transformed the treatment strategy for bladder cancer (BLCA), but primary resistance still occurs in most patients. Recent evidence suggests that neutrophil extracellular traps (NETs) play a key role in cancer therapy resistance, but their specific role in BLCA remains unclear. Methods: An integrated analysis of multiple clinical cohorts receiving ICIs was performed to explore the link between NETs and patient outcomes. Immunofluorescence staining, in vitro co-culture system, scanning electron microscopy, and mouse lung metastasis model were used to evaluate the biological effects of NETs. Proteomics and single-cell transcriptomics analysis were further applied to elucidate the molecular mechanisms. Results: Clinically, NETs abnormally accumulated in BLCA and promoted tumor metastasis and immunotherapy resistance in mice. Mechanistically, NETs upregulated the anti-phagocytic checkpoint STC1 in tumor cells through the TLR2-MAPK-FosL1 axis. Notably, STC1 inhibited antigen presentation by sequestering calreticulin, while its secreted form enhances NET formation, forming a self-reinforcing feedback loop. In addition, secreted STC1 impaired differentiation of CD14+ precursors into mature dendritic cells, further exacerbating immune suppression. Conclusion: This study revealed the critical role of the NETs-STC1 feedback loop in BLCA immunoresistance. Targeting this axis could simultaneously enhance efficacy and safety of immunotherapy, providing a novel translational strategy for overcoming resistance in clinical settings.