Decoding SIGLEC12 in Bladder Cancer: In Silico Profiling of Expression, Tumor–Immune Interactions, and Prognostic Impact

<i>Background and Objectives:</i> Siglec-XII, encoded by SIGLEC12, is a unique sialic acid-binding immunoglobulin-like lectin. It lacks a highly conserved R122 residue for sialic acid recognition in humans. Although it is upregulated in bladder cancer (BCa), its role in tumorigenesis remains largely unexplored. This study aims to investigate the expression patterns of SIGLEC12 in BCa and its correlation with disease features. <i>Materials and Methods</i>: An integrated analysis of transcriptomic data and clinical profiles was conducted using various databases and tools, including UALCAN, GEPIA, TIMER, CAMOIP, and CPADs. The analyses encompassed SIGLEC12 expression, survival rates, immune infiltration levels, promoter methylation, and correlation with drug response. <i>Results</i>: SIGLEC12 expression was higher in both low-grade papillary and high-grade invasive non-papillary BCa. Higher SIGLEC12 expression resulting from low promoter hypomethylation was detected at the stage II-IV of BCa, and was unrelated to disease stages and metastatic stages. Elevated SIGLEC12 expression correlated with increased immune cell infiltration, higher expression of oncogenic and immune checkpoint blockade-related genes, and drug resistance signatures. Mutation analysis confirmed the absence of the canonical R122 missense mutation, indicating that the structural integrity and potential functionality of Siglec-XII are preserved in BCa. <i>Conclusions</i>: SIGLEC12 may have sialic acid recognition functions and serve as a potential early biomarker of BCa.