Before the seeds arrive: pre-metastatic niche orchestration in bladder cancer

Metastatic relapse remains a major cause of mortality in bladder cancer (BCa), yet the biological processes that prepare distant organs for tumor colonization before overt metastasis remain incompletely understood. The pre-metastatic niche (PMN) provides a framework for viewing metastasis as a systemic process in which tumor-derived signals reshape distant immune, stromal, vascular, lymphatic, and metabolic environments before cancer-cell arrival. In BCa, some of the strongest disease-specific evidence implicates extracellular vesicle (EV)-mediated communication, including effects on lymphangiogenesis, vascular permeability, myeloid suppression, stromal crosstalk, and metabolic reprogramming. Additional contributions from myeloid-derived suppressor cells, macrophages, fibroblasts, neutrophil extracellular traps, chemokine networks, and metabolic adaptation may further promote niche permissiveness, although direct BCa evidence remains uneven across mechanisms and metastatic organs. Organotropism to lymph nodes, lung, liver, and bone may reflect the convergence of tumor-intrinsic programs, EV surface molecules, chemokine gradients, and tissue-specific receptivity. Clinically, PMN-associated biomarkers could complement minimal residual disease (MRD) assessment by integrating ctDNA with plasma and urinary EVs and immune, stromal, and metabolic signals. However, such approaches remain investigational and require prospective validation. This review critically evaluates current BCa-specific and cross-cancer evidence, highlights key mechanistic and translational gaps, and proposes a hypothesis-generating MRD-PMN framework for future surveillance and metastatic-interception studies.