To help you understand what is happening when you have cancer, it helps to know how your body works normally. Your body is made up of tiny building blocks called cells. Healthy cells grow and multiply when the body needs them, and die out when the body does not need them.
Cancer is made up of abnormal cells that grow whether they are needed or not. A sarcoma is a cancer that grows in body tissues. It can grow in bones, cartilage, blood vessels, fat, muscles, or tendons and other stringy tissue.
In Kaposi sarcoma (KS), cancer develops from the cells that line lymph or blood vessels. The cancer cells can also grow in the mucous membranes in the nose, mouth, lung, and anus. KS causes purple, brown, or red patches on the skin. These patches are called lesions. KS lesions can spread to other organs in the body, such as the liver and lungs. KS gets its name from Dr. Moritz Kaposi, who first described it.
The lesions can be deforming, but are not usually life-threatening. In most cases, the lesions cause no symptoms. Sometimes, though, the lesions can cause pain or swelling of the skin. When KS involves the liver, lungs, digestive system, or lymph nodes, other symptoms can develop. For example, KS tumors in the lungs can cause breathing problems.
KS may be seen in people with AIDS, but KS can also occur in people without HIV or AIDS.
Infection with human herpes virus 8 (HHV-8) causes KS, although most people infected with HHV-8 do not develop KS. HHV-8 creates an inflammatory state needed for KS to grow. KS is especially aggressive in people with AIDS, because HIV infection weakens the immune system. This allows the tumors to grow more easily.