Kaposi's sarcoma originates in the cells that normally develop into blood or lymph vessels, and usually appears first in the skin. The disease was uncommon in the United States before it began appearing in AIDS patients in the early 1980s. Before AIDS, mild forms of Kaposi's sarcoma -- which rarely caused death -- were observed primarily in middle-aged and elderly men of Mediterranean and European descent. Several forms of Kaposi's sarcoma also occur in children and adults in sub-Saharan Africa. Kaposi's sarcoma arises more commonly in people who are receiving drugs to prevent rejection of transplanted organs, such as the kidney. These drugs suppress the immune system.
For these reasons, Kaposi's sarcoma is often classified into one of four groups:
- classic (For more information about classic Kaposi's sarcoma, visit the Rare Solid Tumors section of this Web site.)
- African (endemic)
- transplant-associated (seen especially in people with kidney transplants)
- AIDS-associated (epidemic)
Kaposi's sarcoma and Pneumocystis pneumonia were the first diseases associated with AIDS. For many years, Kaposi's sarcoma has been the most common cancer in AIDS patients; the incidence has decreased, however, in the last decade.
Light-skinned people usually develop pink, or red to purple lesions; in dark-skinned people the lesions often appear brown or black. The lesions are caused by abnormal blood vessels that grow in a distorted and disorganized fashion, and by blood cells that leak out of these blood vessels. About a third of patients with AIDS-associated Kaposi's sarcoma develop lesions inside the mouth. AIDS-associated Kaposi's sarcoma is often much more aggressive than classic Kaposi's sarcoma.
Kaposi's sarcoma lesions are generally not painful, but they sometimes do cause pain that can be debilitating. Lesions on the feet, for example, may prevent a patient from walking. These lesions are treatable and usually not life-threatening unless the internal organs are extensively involved.
