A 77-year-old man developed pulmonary tumor thrombotic microangiopathy (PTTM) 2 days after undergoing transurethral resection for urothelial carcinoma (G3) of the urinary bladder and died of respiratory failure 6 days later. Histological findings demonstrated marked intimal fibrocellular proliferation, fibrin thrombi, and both cancer cells and fibrin thrombi in the arteries of the lungs, findings consistent with PTTM. Prominent stenosis in arteries smaller than 300 μm was also seen. The Ki-67 labeling index of primary and metastasized cancer cells was 62.4 % and 70.2 %, respectively. The membranes of metastasized cancer cells expressed E-cadherin, similar to membranes in the urinary bladder. An aggressive PTTM course is affected by intimal fibrocellular proliferation and the high cell proliferation of cancer cells. Furthermore, prominent stenosis in small arteries and membranous staining of E-cadherin of metastasized cells suggest that cancer cells formed clusters by maintaining adhesion molecules and migrated into the arteries of the lungs, where they easily caused damage to the endothelium of small arteries, in contrast to dispersed cancer cells.