What is bladder cancer?
The normal bladder
To understand bladder cancer, it helps to know about the normal structure and function of the bladder. The bladder is a hollow organ that stores urine. Urine is made in the kidneys and flows into the bladder through thin tubes called ureters. Urine leaves the bladder through another tube called the urethra. In women the urethra is very short. In men it is longer and passes through the prostate gland to the tip of the penis.
The urinary system
The wall of the bladder is made of 4 main layers. The innermost layer of the bladder is lined with cells called urothelial cells. The same type of cells also lines parts of the kidneys, the tubes connecting the kidneys to the bladder (ureters), and the urethra.
Most bladder cancers start in this inner lining layer and grow into or through the other layers of the bladder. As the cancer grows through the layers it becomes more advanced and harder to treat.
Types of bladder cancer
Bladder cancers are grouped into several types by the way the cancer cells look under a microscope. The type of bladder cancer you have can affect your treatment options because different types need different treatments.
Transitional cell carcinoma: This is by far the most common type of bladder cancer. It starts in the cells that line the inside of the bladder – the urothelial cells. It is also called urothelial carcinoma.
Within this group there are subtypes. Papillary cancers grow like fingers from the inner bladder lining toward its hollow center, while flat cancers do not grow toward the center.
These tumors are also named based on whether they have grown into the bladder wall. If they grow deeper into the bladder wall they are called invasive; if not, they are non-invasive.
Squamous cell carcinoma: This type is much less common and is usually invasive.
Adenocarcinoma: This type is also much less common and almost all are invasive.
Small-cell carcinoma: A very small number of bladder cancers are of this type. These cancers often grow quickly.
The rest of this document deals with transitional cell (urothelial) cancers of the bladder.
Last Medical Review: 12/03/2012
Last Revised: 01/21/2013