Background <p>The role of RAP1GAP in tumor progression has garnered increasing attention; however, its prognostic value and immunological influence across various cancers remain uncertain. Our study presents a pan-cancer analysis to investigate its involvement in oncogenesis and immune regulation.</p> Methods <p>Public databases were utilized to assess RAP1GAP expression across cancers. Cox regression analysis evaluated its prognostic value, while Pearson correlation examined associations with genomic heterogeneity, tumor stemness, immune cell infiltration, and immune checkpoints. Immunohistochemical staining of bladder cancer and adjacent tissues assessed RAP1GAP expression and clinical correlations.</p> Results <p>RAP1GAP expression is differentially expressed in a variety of tumor types and predicts a better or worse prognosis for tumor patients. It was strongly linked to genomic heterogeneity and tumor stemness in multiple cancers. Immunohistochemistry showed increased RAP1GAP expression in bladder cancer. Immune cell analysis revealed high RAP1GAP expression was associated with greater infiltration of plasma cells, naive CD4 ⁺ T cells, Tregs, and eosinophils, while low expression correlated with increased CD8 ⁺ T cells, activated memory CD4 ⁺T cells, and M1 macrophages.</p> Conclusion <p>RAP1GAP is a potential prognostic biomarker and immune regulator, with promising implications as an immunotherapeutic target for bladder cancer.</p>