The role of serum lymphocyte-based biomarkers, such as the neutrophil-to-lymphocyte (NLR), lymphocyte-to-monocyte (LMR), and platelet-to-lymphocyte (PLR) ratios, was previously studied in patients with muscle-invasive bladder cancer (MIBC) treated with radical cystectomy but remains underexplored in patients treated with trimodal therapy (TMT).