Kaposi sarcoma is a cancer in which red or purple patches grow below the surface of the skin or in the mucous membranes of the mouth, nose, throat, or other organs. The patches are made of a combination of cancer cells and blood cells. In many instances the patches are painless, but in other cases they may cause painful swelling. As long as Kaposi sarcoma remains within the skin, it is usually not a life-threatening or disabling disease, although the patches may be unattractive. However, if the cancer spreads to the digestive tract, lungs, or liver, it can become very serious.
Kaposi sarcoma is caused by a virus called Kaposi sarcoma-associated herpes virus (KSHV) or human herpes virus 8 (HHV-8). Researchers don't know how many people are infected with this virus. Studies in the United States have found infection rates as low as 3.5% and as high as 25% in different parts of the country. In Africa, the infection rate is greater than 50%. Even in areas where infection rates are high, however, most people who are infected with the virus do not develop Kaposi sarcoma, and when people with normal immune systems do get it, it tends to be a relatively mild disease. However, when the immune system is impaired, the likelihood that a person who is infected with the virus will get Kaposi sarcoma is greater, and the disease itself may become more serious.
Prior to the start of the AIDS epidemic, Kaposi sarcoma was a rare disease. Three different forms of the disease were known, each affecting a different population group: middle-aged to elderly men of Mediterranean or Jewish heritage (this form of the disease is known as classic Kaposi sarcoma), young adult African men, and organ transplant recipients who were taking drugs that suppress the immune system.
Among organ transplant recipients, about one in 200 develops Kaposi sarcoma. Although this risk is higher than that in the general population, the increase is not as great as the increase in risk of other skin cancers faced by organ transplant recipients. All organ transplant recipients should be receiving regular examinations by a dermatologist because of their increased risk of developing a variety of skin cancers, some of which need to be detected early in order to be treated successfully.