Objective: Tumor-infiltrating lymphocytes (TILs) have been shown to predict outcomes in several cancers. This study aimed to evaluate the density and location of regulatory T cells (Tregs) using immunohistochemistry (IHC) in urothelial carcinomas (UC) of the bladder and to assess their prognostic value.

Material and Methods: We have retrospectively collected all cases of UC of the bladder infiltrating at least the lamina propria, diagnosed in our pathology department between 2011-2021. Specimens were stained for CD3 and CD25. TILs were assessed separately in the tumor core and the stroma. The median TIL count was used as a cut-off to classify cases into low- or high-density groups.

Results: A total of 30 cases were included in the study. The median age of the patients was 65 years, with a male-to-female ratio of 9:1. The distribution of TILs was heterogeneous across locations among patients. CD3+ (p=0.035) and CD25+ (p=0.051) TILs were predominantly observed in the stroma. The density of CD25+ and CD3+ TILs were not associated with clinicopathological features. Multivariate analysis revealed that advanced histological stage and a high density of regulatory CD25+ T lymphocytes were predictive factors of poorer event-free survival (respectively p=0.041 and p=0.052).

Conclusion: Regulatory T cells appear to predict worse survival outcomes. Further studies are needed to confirm their prognostic value.