Kaposi's sarcoma is cancer that forms in the lining of the blood and lymph. Tumors (lesions) of Kaposi's sarcoma are usually in the form of painless purple spots on the legs, feet or face. Injuries can also occur in the genital area, in the mouth, or in the lymph nodes. Severe Kaposi's sarcoma can cause damage to the digestive tract and lungs. The underlying cause of Kaposi's sarcoma is an infection with a virus called human herpesvirus 8. In healthy people, HHV-8 infection usually does not cause symptoms because the immune system keeps them under control. However, in people whose immune systems are weakened, HHV-8 can trigger Kaposi's sarcoma.
People infected with the human immunodeficiency virus (HIV), which causes AIDS, are at greatest risk of acquiring Kaposi's sarcoma. The damage caused by HIV to the immune system allows the cells harboring HHV-8 to multiply. Through unknown mechanisms, characteristic lesions are formed. Organ transplant recipients who use immunosuppressive drugs to prevent rejection of the transplant are also subject to Kaposi's sarcoma. However, in this population, the disease tends to be less severe and easier to control than in people with AIDS.
Another type of Kaposi's sarcoma occurs in elderly men of European, Mediterranean and Middle Eastern descent. This is known as classic Kaposi's sarcoma, this cancer is slow and usually causes a few serious problems. The fourth type of Kaposi's sarcoma, which affects humans of all ages, occurs in equatorial Africa.