CD74 expression is increased in high‐grade,invasive urothelial carcinoma of the bladder

This study aimed to identify the clinicopathological features of bladder cancer patients with high CD74 expression, as milatuzumab humanized anti‐CD74 antibody is being evaluated in clinical trials for hematological malignancies. Expression of CD74 was examined in 342 urothelial carcinomas of the bladder, and two urothelial carcinoma cell lines by immunohistochemistry and western blotting, respectively. CD74 was overexpressed in 192 (56.1%) of the 342 cancer tissues, although it was not expressed in the cancer cell lines. CD74 staining was intense in tumor cells and inflammatory cells in the tumor stroma, but not in normal urothelium. CD74 expression was significantly associated with older age at diagnosis (≥68 years, P = 0.048), high World Health Organization grade (P = 0.019), advanced stages (P = 0.001) and non‐papillary growth pattern (P = 0.040). CD74 expression was also correlated with the absence of tumor‐infiltrating inflammatory cells (P < 0.001) and the presence of tumor‐associated inflammatory cells (P = 0.017). However, CD74 expression was not related to recurrence‐free and overall survivals in primary and subgroup analyses. In conclusion, urothelial bladder carcinomas with high CD74 expression are characterized by older age, high World Health Organization grade, non‐papillary growth and advanced stages.