Overview of the study design. (A) Data sources used in this study; (B) Correlations between Siglec15 and pan-cancer immunological elements. TIICs were estimated using ssGSEA algorithm. (C) Correlation between Siglec15 and the immunological status of the tumor microenvironment in BLCA. The immunological status includes immunomodulators, steps of the cancer-immunity cycle, immune checkpoints, T cell-inflamed score, and TIICs. (D) Role of Siglec15 in predicting the molecular subtypes in BLCA. (E) Role of Siglec15 in predicting therapeutic responses to immunotherapy, neoadjuvant/adjuvant chemotherapy, targeted therapy, EGFR therapy, and radiotherapy in BLCA. (F) Development of an immune risk score; (G) Sankey plot displaying the main results in this study. TIICs: tumor-infiltrating immune cells, IF: immunofluorescence.