Single-cell and spatial atlas unveil tumor-specific microenvironment convergence and a prognosis-associated PLXDC1+ myofibroblast population in metastatic bladder cancer

While single-cell technologies have advanced bladder cancer research, the microenvironment of lymph node metastases and its role in progression remain unclear. We aimed to elucidate dynamic tumor-microenvironment interactions across metastatic and primary sites, identify poor-prognosis features, and uncover novel therapeutic targets. We profiled matched single-cell and spatial transcriptomic samples from lymph node-metastasized bladder cancer to construct a high-resolution atlas. Bioinformatic analyses were used to inferred ligand-receptor interactions, regulatory networks, and spatial co-localization. Integration with multiple prognostic cohorts revealed key cell subpopulations linked to tumor biology and poor outcomes. Our atlas included 32 samples, 61 cell subtypes, key ligand signals (e.g., TGFB1, OSM, IFNG), 343 transcription factors, 188 co-localization events, over 1,000 spatially validated interactions, and 21 cell niches. Tumor-driven convergence was observed across distinct microenvironments. Notably, a pericyte-like myofibroblast subtype, myoCAF_PLXDC1, was enriched in malignant tissues, associated with poor prognosis, and exhibited enhanced angiogenic but reduced chemotactic activity compared to myoCAF_CCL21. Its phenotype was linked to intracellular regulators (PRRX1 and MXD4) and extracellular signals (IFNG and TGFB1). Spatially, myoCAF_PLXDC1 co-localized with ITGA8+ endothelial cells and enriched in tumor regions. This study offers a comprehensive resource for lymph node-metastasized bladder cancer and identifies PLXDC1+ fibroblasts co-localized with ITGA8+ ECs as potential components of a tumor-specific vascular niche and therapeutic target.