Objective To evaluate the role of macrophage infiltration in the differentiation 
process of ureteral polyps and cancers. Methods This retrospective 
immunohistochemical study analysed archival samples of pathologically-confirmed 
specimens of low- and high-grade ureteral cancer, ureteral papilloma and 
ureteral polyps. The samples were immunohistochemically stained for cluster of 
differentiation (CD)4, CD8, CD16, CD25, CD56 and CD68 using immunofluorescence 
in order to identify different T-lymphocyte populations and macrophages. Results 
A total of 70 specimens were included in the analysis: 21 specimens of ureteral 
cancer, 17 specimens of ureteral papilloma, and 32 specimens of ureteral polyps. 
The largest proportion of CD4+CD25+ regulatory T cells was observed in the 
low-grade ureteral cancer group and almost none were observed in ureteral 
papillomas. The largest proportion of CD8+ cytotoxic T-lymphocytes was observed 
in the ureteral polyps. The largest proportion of CD56+ natural killer cells was 
detected in the ureteral polyps, with very low levels observed in the other 
three groups. The largest proportion of CD16+CD68+ macrophages was observed in 
the high-grade ureteral cancer group, which was significantly higher than that 
observed in the ureteral papillomas. Conclusions This study revealed that 
CD16+CD68+ macrophages appear to participate in ureteral neoplastic 
transformation.