Density of tumor-infiltrating granzyme B-positive cells predicts favorable prognosis in dogs with transitional cell carcinoma

Although tumor-infiltrating lymphocytes (TILs) play a key role in anti-tumor immunity, their involvement in canine transitional cell carcinoma (TCC) is not well-documented. The objective of this study was to investigate the association between TIL number and prognosis in dogs with urinary bladder TCC. Immunohistochemical analysis of CD3 and granzyme B was performed using canine TCC (n = 32) and normal bladder (n = 10) tissues. The numbers of CD3+ and granzyme B+ cells located in peritumoral stroma of canine TCC were significantly higher than those in normal controls. In TCC cases, the number of CD3+ TILs was not significantly related to prognosis, whereas the abundant granzyme B+ TILs were associated with favorable outcome. Since granzyme B+ TILs were not associated with the tumor stage, the presence of granzyme B+ TILs may be an independent prognostic factor. These results suggest that granzyme B+ TILs play a role in anti-tumor immunity and inhibit tumor progression in canine TCC.