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The bladder is an expandable, hollow organ in the pelvis that stores urine (the body’s liquid waste) before it leaves the body during urination. The urinary tract is made up of the kidneys, ureters, bladder, and urethra and is lined with a layer of cells called the urothelium. This layer of cells is separated from the muscularis propria (bladder muscles) by the lamina propria (a thin, fibrous band).
Bladder cancer begins when normal cells in the bladder begin to change and grow uncontrollably, forming a mass called a tumor. A tumor can be benign (noncancerous) or malignant (cancerous, meaning is can spread to other parts of the body). It is described as either noninvasive or invasive. Noninvasive cancer does not spread through the lamina propria, and invasive cancer can spread through the lamina propria. Noninvasive cancer may also be called superficial cancer, although that 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 and can often be managed with surgery to remove tumors and chemotherapy (see Treatment). Invasive cancer is subdivided as either cancer that only grows into the lamina propria or cancer that grows into the muscle layer. Both invasive and noninvasive bladder cancers have the possibility of spreading into the bladder muscle or to other parts of the body.
There are three main types of bladder cancer, depending on the type of cell where the cancer begins:
Urothelial carcinoma. Urothelial carcinoma is a new term for this type of bladder cancer. It was previously called transitional cell carcinoma or TCC. Urothelial carcinoma accounts for about 90% of all bladder cancers and begins in the urothelium. A tumor of this type may be described further using one of the four subcategories explained below.
Non-muscle-invasive/superficial urothelial carcinoma. This subtype of urothelial carcinoma is limited to the urothelium and is non-muscle-invasive, meaning it has not spread to the muscle layer. It may spread into the lamina propria beneath the transitional cells. This is sometimes called invasive, though it is not the deeply invasive type that can spread to the muscle layer.
Muscle-invasive urothelial carcinoma (often called invasive urothelial carcinoma). This subtype of urothelial carcinoma spreads to the bladder's muscularis propria and sometimes to the fatty layers or surrounding tissue outside the muscle.
Papillary urothelial carcinoma. Papillary is a word that describes a growth that is like a small polyp or flower-shaped cluster of cancer cells. A noninvasive papillary tumor grows into the hollow center of the bladder on a stalk. Invasive papillary urothelial carcinoma can spread into the lamina propria or muscle layer.
Flat urothelial carcinoma. Noninvasive flat urothelial carcinoma (also called carcinoma in situ, or CIS) grows in the layer of cells closest to the inside of the bladder and appears as flat lesions on the inside surface of the bladder. Invasive flat urothelial carcinoma may invade the deeper layers of the bladder, particularly the muscle layer.
Squamous cell carcinoma. This type accounts for about 4% of all bladder cancers and starts in squamous cells, which are thin, flat cells.
Adenocarcinoma. This type accounts for about 2% of all bladder cancers and begins in glandular cells.
All three major types of bladder cancer can metastasize (spread) beyond the bladder. If the tumor has spread into the surrounding organs (the uterus and vagina in women, the prostate in men, and/or nearby muscles), it is called locally advanced disease. The area outside of these organs where bladder cancer usually spreads is the lymph nodes in the pelvis. If it has spread into the liver, bones, lungs, or other parts of the body, these are distant metastases and the cancer may be called advanced disease.
There are other, less common types of cancer that arise in the bladder, including sarcoma (which begins in the muscle layers of the bladder) and small cell anaplastic cancer (a rare type of bladder cancer that is likely to spread to other parts of the body).
Looking for More of an Overview?
If you would like additional introductory information, explore the following item on Cancer.Net:
- ASCO Answers Fact Sheet: Read a one-page fact sheet (available in PDF) that offers an easy-to-print introduction for this type of cancer.
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- Medical Illustrations
- Risk Factors
- Staging with Illustrations
- Side Effects
- After Treatment
- Questions to Ask the Doctor
- Current Research
- Patient Information Resources
- Clinical Trials Resources
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