The bladder is a hollow organ in the lower part of the abdomen. It is shaped like a small balloon and has a muscular wall that allows it to get larger or smaller. The urine passes from the two kidneys into the bladder through two tubes called ureters. The bladder is emptied through another tube called the urethra.
There are three types of bladder cancer that begin in cells in the lining of the bladder: transitional cell carcinoma; squamous cell carcinoma; and adenocarcinoma.
Cancer that is confined to the lining of the bladder is called superficial bladder cancer. Cancer that begins in the transitional cells may spread through the lining of the bladder and invade the muscle wall of the bladder or spread to nearby organs and lymph nodes; this is called invasive bladder cancer.
SEER Cancer Stat Facts: Bladder Cancer. National Cancer Institute. Bethesda, MD, http://seer.cancer.gov/statfacts/html/urinb.html