Cancer is a disease in which cells grow in an abnormal way. Normally, the cells divide in a controlled manner. If cells keep dividing when new cells are not needed, a mass of tissue called a tumor forms.
A tumor can be benign or malignant. A benign tumor is not cancer and will not spread to other parts of the body. A malignant tumor is cancer. Cancer cells invade and damage tissue around them. They can also enter the lymph and blood streams, spreading to other parts of the body. Bladder cancer is the development of malignant cells in the bladder.
Normal Anatomy and the Development of Bladder Cancer
The urinary bladder is a hollow, muscular organ located in the pelvic cavity. The bladder has 4 layers of muscular tissue. Urothelial cells line the inside of the bladder and urinary tract. Urine produced by the kidney travels down tubes called ureters and into the bladder. The bladder then stores urine until it can be passed from the body through the urethra. In females, the bladder is in front of the vagina. In males it is in front of the rectum. The bladder is surrounded by nerves, connective, and fatty tissue, as well as blood and lymph vessels, which can all be affected by cancer.
Cell division and cell death are a normal process in the body to replace old or damaged cells. The inside lining of the bladder is an area that may have a higher rate of cell turnover because it is exposed to waste products in the urine. The turnover and irritation of the bladder wall can be increased with chronic conditions of the bladder and exposure to toxins.
Bladder cancer can cause bleeding or interfere with bladder function. If it grows beyond the bladder walls, the cancer can penetrate nearby structures, such as the rectum, vagina, or intestines, and interfere with their function. It can also spread to lymph nodes or blood vessels, which can carry cancer cells to other areas of the body. The most common sites for metastatic bladder cancer are the lymph nodes in other parts of the body, the bones, lungs, liver, and peritoneum (tissue that lines the abdominal cavity).
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Types of Bladder Cancer
Almost all bladder cancers are transitional cell or urothelial carcinomas. This type of cancer develops in the innermost layer of the bladder which is made of urothelial (transitional) cells.
There are 2 types of transitional cell carcinomas:
Papillary—Finger-like projections that grow from the surface of the bladder wall into the open space of the bladder. They generally do not grow into the deeper layers of the bladder wall. If they do, treatment response is usually more effective.
Flat—They are flat and on the inner layer of the bladder.
Bladder cancer is described by the invasiveness of the tumor. In situ, or nonmuscle-invasive cancer, only affects local tissue. This means the cancer is contained to the urothelium and has not spread. In situ cancer treatment is local and offers the best chance for cure. Muscle-invasive cancers spread into the muscle layers of the bladder. Depending on how long the cancer has been growing, invasion can occur into deeper muscle layers, adjacent tissue, or distant sites in the body.
Other types of bladder cancer are also classified by the tissue they start in. Types of bladder cancer include:
Squamous cell carcinoma—Flat cells found on the inner wall. This type of cancer is almost always invasive.
Adenocarcinoma—Cells that form in the glandular tissue. This type of cancer is almost always invasive.
Small cell carcinoma—Rare and arise from nerve cells in the glands. This type of cancer grows fast, but can be treated.
Sarcoma—Very rare and arise from the muscular tissue of the bladder.