UBC is cancer of the lining of the urinary system. It begins in urothelial cells, which line the inside of the bladder and other parts of the urinary tract. These cells overgrow and form a tumor. This type of cancer occurs most often in the bladder, but can occur anywhere that urothelial cells are present, including the urethra, ureters and kidneys.There are three main types of urothelial bladder cancer: urothelial carcinoma (also known as transitional cell carcinoma), squamous cell carcinoma and adenocarcinoma. Urothelial carcinoma is the most common type of bladder cancer cancer in the United States; it accounts for up to 90% of all bladder cancers and up to 10% of all kidney cancers. Squamous cell carcinoma forms due to chronic infection or chronic inflammation in the bladder, such as when a foley catheter is left in place for an extended time. This type of cancer is more common in other parts of the world where parasitic bladder infections more frequently occur. Adenocarcinoma is rare and forms from the mucus-secreting glands in the bladder.