If cells within the bladder start to grow out of control and do not respond to signals from the rest of the body, bladder cancer can develop. The most common type of bladder cancer arises from the urothelial cells of the bladder lining, and are collectively called urothelial tumours.

Under the microscope, bladder cancer cells typically have large, abnormal nuclei of varying shapes, signs of cell division (indicating rapid tumour growth) and the thickness of the urothelial cell layer is increased. The grade of the bladder cancer is dependent on the presence/ absence of aggressive features, whereas the staging is based upon how far the cancer cells have spread through the bladder wall.