In bladder cancer, cells that make up the bladder begin to grow out of control. As more cancer cells develop, they form a tumor and, over time, spread to other parts of the body.
An organ in the lower pelvis called the bladder has flexible, muscular walls that can stretch to hold urine and squeeze to release it. Urine is the main function of the bladder. The 2 kidneys produce urine and transport it to the bladder through 2 tubes called ureters. Urine is then forced out of your bladder through a tube called the urethra when you urinate.