Introduction:
Urological cancers pose a significant global health burden. Alterations in immunoglobulin G(IgG) N-glycosylation are implicated in cancer pathogenesis, but their causal role remains unclear. This study aimed to explore the potential causal associations between 77 specific IgG N-glycan traits (IGPs) and the risks of bladder, kidney, and prostate cancer.

Material and methods:
We conducted a two-sample Mendelian randomization (MR) study using summary-level data. Genetic instruments for IGPs were obtained from a genome-wide association study (GWAS) of European descent. Outcome data were sourced from the FinnGen consortium. The inverse-variance weighted (IVW) method was the primary analysis, supplemented by multiple sensitivity analyses (MR-Egger, weighted median, MR-PRESSO, and MR-RAPS). The Steiger test was used to confirm causal direction.

Results:
After a strict false discovery rate (FDR) correction, one association remained statistically significant. Using the IVW method, genetically predicted higher levels of IGP23 were significantly associated with a decreased risk of bladder cancer (OR = 0.78, P = 4.7e-04, FDR = 0.037). Thirteen other nominal associations (P < 0.05) were also identified, suggesting potential risk or protective factors for urological cancers (e.g., IGP10 for prostate cancer; IGP52, IGP73 for kidney cancer), although these did not withstand multiple testing correction. Sensitivity analyses indicated no significant directional pleiotropy.

Conclusions:
Our study provides robust genetic evidence for a causal protective effect of the IgG N-glycan trait IGP23 on the risk of bladder cancer. While other nominal associations require further investigation, our findings highlight IGP23 as a key candidate for future mechanistic research and potential biomarker development in bladder cancer.