We report a rare case of plasinacytoid urothelial carcinoma (PUC) or the urinary bladder. A 50-year-old man complained of pollakiuria and urinary incontinence. MRI detected a bladder tumor Invading the rectum and bilateral hydroureteronephrosis. Radical cystectomy with partial resection of the rectum was performed, and ileus due to peritoneal dissemination occurred 2 years after surgery. He died of the disease 42 months after the initial presentation. Histologically. urothelial carcinoma In situ with a focal invasive urothelial carcinoma (IUC) component and widely spread PUC was observed. There was no lymph node metastasis. PUC cells had eccentrically placed nuclei and eosinophilic cytoplasm resembling plasmacytoma cells, and proliferated with a single-cell infiltrative pattern to the outside of the bladder. IUC cells with intracytoplasmic lumina were focally intermingled with PUC cells. Immunohistochemically, PUC cells were positive for cytokeratin 7, epithelial membrane antigen, and CA19-9. but negative for cytokeratin 20, E-cadherin, p63, and lymphoid markers. The Ki-67 labeling index of PUC cells was 9.3%. IUC containing intracytoplasmic lumina showed intermediate features of conventional IUC and PUC morphologically and immunohistochemically. PUC is a distinct entity of bladder cancer with a high propensity for invasion and poor prognosis. (C) 2008 Elsevier GmbH. All rights reserved.