The normal bladder

Your bladder is a hollow pelvic organ with flexible, muscular walls that stores urine. The average adult bladder holds about 2 cups of urine. Urine is made by the kidneys and is then carried to the bladder through tubes called ureters. The urine leaves the bladder through another tube called the urethra. In women, the urethra is a very short tube that ends just in front of the vagina. In men, the urethra is longer. It passes through the prostate gland and the penis, and ends at the tip of the penis.

The wall of the bladder has several layers. A layer of cells lines the inside of the kidney, ureter, bladder, and urethra. These cells are called urothelial or transitional cells, and so this layer is called the urothelium or transitional epithelium. Beneath the urothelium, there is a thin layer of connective tissue called the lamina propria. Next, there is a layer of muscle tissue called the muscularis propria. Beyond this muscle, another zone of fatty connective tissue separates the bladder from other nearby organs. These layers are very important in understanding bladder cancer. As the cancer penetrates or grows through these layers into the wall of the bladder, it becomes harder to treat.

Types of bladder cancer

Bladder tumors are grouped into several types by how their cells look under a microscope. The type of bladder cancer you have can affect your treatment options. This is because different types can respond differently to treatments such as radiation and chemotherapy. The main types of cancers that affect the bladder are:

• transitional cell carcinoma (also called urothelial carcinoma)
• squamous cell carcinoma
• adenocarcinoma
• small cell

These same types of cancer can also grow in other places in the urinary tract, such as the lining of the, kidney (called the renal pelvis), the ureters, and the urethra. In fact, patients with bladder cancer sometimes have a similar tumor in the lining of the kidneys, ureters, or urethra. Therefore, when someone is found to have a cancer in one part of their urinary system, the entire urinary tract needs to be checked for tumors.

Transitional cell carcinoma

This is the most common type of bladder cancer. The cells from transitional cell carcinomas look like the urothelial cells that line the bladder. More than 97% of bladder cancers are this type. These tumors are divided into grades based on how abnormal the cells look under the microscope. If the cells look similar to normal cells, the cancer is called a low-grade cancer. When the cells look very abnormal, the cancer is high-grade. In the past, some cancers were given a grade in between these -- grade 2. This category is no longer being used. Many of the cancers that would have been called grade 2 in the past are now put in the high-grade grouping. Lower-grade cancers tend to grow more slowly and have a better outcome than higher-grade cancers.

Another factor that is important in predicting outlook is whether or not the cancer is invasive. Transitional cell cancers start in the cells lining the bladder. If the cancer stays in this layer of cells, without growing into the deeper layers, it is called noninvasive. If the cancer grows beneath the top layer, into the lamina propria or even deeper into the muscle layer, it is called invasive. Invasive cancers are more likely to spread and are harder to treat. You may also see a bladder cancer described as superficial or non-muscle invasive. The term includes both noninvasive tumors as well as any invasive tumors that have not grown into the main muscle layer of the bladder

Transitional cell carcinomas are also divided into 2 subtypes, papillary and flat.

Papillary tumors have slender finger-like projections that grow from the inner surface of the bladder toward the hollow center. They can look like a type of cactus plant. Often, papillary tumors grow toward the center of the bladder without growing into the deeper bladder layers. These tumors are called noninvasive papillary cancers. Because this tumor tends to have a good outcome, a very low-grade noninvasive papillary cancer is sometimes called papillary neoplasm of low-malignant potential. If a papillary carcinoma is growing into the deeper layers of the bladder wall, it is called invasive.

Flat carcinomas do not grow toward the hollow part of the bladder at all. A flat tumor may only involve the layer of cells in the bladder lining (closest to the hollow part of the bladder). This type of tumor is known as a noninvasive flat transitional cell carcinomas or a flat carcinoma in situ (CIS). Some flat carcinomas can go on to grow into the deeper layers of the bladder, even into the muscle layer. These are then called invasive transitional cell carcinomas.

Squamous cell carcinoma

In the United States, only about 1% to 2% of bladder cancers are squamous cell carcinomas. Under a microscope, the cells look much like the flat cells that are found on the surface of the skin. Nearly all squamous cell carcinomas are invasive.

Adenocarcinoma

Only about 1% of bladder cancers are adenocarcinomas. The cancer cells have a lot in common with gland-forming cells of colon cancers. Nearly all adenocarcinomas of the bladder are invasive.

Small-cell carcinoma

Less than 1% of bladder cancers are small-cell carcinomas. Chemotherapy for these cancers is similar to that used for small-cell carcinoma of the lung.

Other cancers

Cancers rarely start in the muscle cells of the bladder. But when they do, these cancers are called sarcomas. More information about sarcomas can be found in our documents: Sarcoma - Adult Soft Tissue Cancer and Rhabdomyosarcoma.

Last Medical Review: 01/27/2009
Last Revised: 5/13/2009