Prognostic Impact of APOBEC3B Expression for Tumor-infiltrating Cytotoxic T cells in Metastatic Urothelial Carcinoma

Abstract Background: The APOBEC3B enzymes are endogenous carcinogenic mutagens. Metastatic urothelial carcinomas often harbor APOBEC3B-mediated mutations in which tCw to T or G substitution occurs. A high mutation burden in urothelial carcinoma can increase T-cell immunity against cancer cells, affecting prognosis. In this study, we aimed to evaluate patient survival and CD8+ T-cell density according to APOBEC3B expression in patients with metastatic urothelial carcinoma who underwent cytotoxic chemotherapy.Methods: We performed a retrospective study in 94 patients with urothelial carcinoma who were treated with the first line palliative chemotherapy. Immunohistochemistry staining was performed to evaluate APOBEC3B expression and CD8+/CD3 ratio of tumor-infiltrating lymphocytes. Survival curves according to APOBEC3B expression were generated using the Kaplan–Meier method and compared using the log-rank test. The correlation between APOBEC3B expression and tumor-infiltrating lymphocytes was analyzed using Pearson’s chi-squared test. Results: A high APOBEC3B expression was detected in 71 of the 94 patients (75.5%). The median overall survival of patients with high APOBEC3B expression (15 months) was longer than that of patients with low APOBEC3B expression (p = 0.045 by log-rank test). The hazard ratio based on the Cox regression analysis was 0.252 (95% confidence interval 0.082–0.781, p = 0.017). APOBEC3B expression was associated with the CD8+/CD3+ ratio of tumor-infiltrating lymphocytes (odds ratio 2.914, 95% confidence interval 1.030–8.249, p = 0.039).Conclusions: APOBEC3B expression was an independent prognostic factor in patients with metastatic urothelial carcinoma treated with platinum-based chemotherapy. Tumor-infiltrating cytotoxic T cells correlated with APOBEC3B expression.