About the bladder and bladder cancer
The bladder is an expandable, hollow organ in the pelvis that stores urine before it leaves the body during urination. This function makes the bladder an important part of the urinary tract. The urinary tract is also made up of the kidneys, ureters, and urethra.
The bladder, like other parts of the urinary tract, is lined with a layer of cells called the urothelium. This layer of cells is separated from the bladder wall muscles, called the muscularis propria, by a thin, fibrous band called the lamina propria.
Bladder cancer begins when healthy cells in the bladder lining, most commonly urothelial cells, change and grow uncontrollably, forming a mass called a tumor. A tumor can be cancerous or benign. A cancerous tumor is malignant, meaning it can grow and spread to other parts of the body. A benign tumor means the tumor can grow but will not spread.
Types of bladder cancer
The type of bladder cancer depends on how it looks under the microscope. The three main types of bladder cancer are:
Urothelial carcinoma. Urothelial carcinoma accounts for about 90% of all bladder cancers. It begins in the urothelial cells found in the lining the bladder. Urothelial carcinoma is the common term for this type of bladder cancer; however, it was previously called transitional cell carcinoma or TCC.
Squamous cell carcinoma. Squamous cells develop in the bladder lining in response to irritation and inflammation. Over time these cells may become cancerous. Squamous cell carcinoma accounts for about 4% of all bladder cancers.
Adenocarcinoma. This type accounts for about 2% of all bladder cancers and develops from glandular cells.
There are other less common types of bladder cancer, including sarcoma and small cell anaplastic cancer. Sarcoma begins in the fat or muscle layers of the bladder. Small cell anaplastic cancer is a rare type of bladder cancer that is likely to spread to other parts of the body.
Ways of describing bladder cancer
In addition to its cell type, bladder cancer may be described as noninvasive, non-muscle-invasive, or muscle-invasive.
Noninvasive. This type of bladder cancer usually does not extend through the lamina propria. Noninvasive cancer may also be called superficial cancer, although this term is being used less often because it may incorrectly imply that this type of cancer is not serious. Noninvasive bladder cancer is less likely to spread to other parts of the body than other types of bladder cancer.
Non-muscle-invasive. Non-muscle-invasive bladder cancer typically has only grown into the lamina propria. It is called invasive, but it is not the deeply invasive type that can spread to the muscle layer (see below).
Muscle-invasive. Muscle-invasive bladder cancer has grown into the bladder's wall muscle and sometimes into the fatty layers or surrounding tissue outside the bladder.
It is important to note that both noninvasive and non-muscle-invasive bladder cancers have the possibility of spreading into the bladder muscle or to other parts of the body. Additionally, all cell types of bladder cancer can spread beyond the bladder through a process known as metastasis.
If a bladder tumor has spread into the surrounding organs, such as the uterus and vagina in women, the prostate in men, and/or nearby muscles, it is called locally advanced disease. Bladder cancer also often spreads to the lymph nodes in the pelvis. If it has spread into the liver, bones, lungs, lymph nodes outside the pelvis, or other parts of the body, the cancer is called metastatic disease. This is described in more detail in the Stages and Grades section.
Looking for More of an Overview?
If you would like additional information, read a one-page ASCO Answers Fact Sheet, available as a PDF, that offers an easy-to-print introduction to this type of cancer. Please note this link will take you to another section on Cancer.Net.