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Cancer starts when cells in the body begin to grow out of control. Cells in nearly any part of the body can become cancer and can spread. To learn more about how cancers start and spread, see What Is Cancer?

Kaposi sarcoma (KS) is a cancer that develops from the cells that line lymph or blood vessels. It usually appears as tumors on the skin or on mucosal surfaces such as inside the mouth, but these tumors can also develop in other parts of the body, such as in the lymph nodes (bean-sized collections of immune cells throughout the body), the lungs, or digestive tract.

The abnormal cells of KS form purple, red, or brown blotches or tumors on the skin. These affected areas are called lesions. The skin lesions of KS most often show on the legs or face. They may look bad, but they usually cause no symptoms. Some lesions on the legs or in the groin area may cause the legs and feet to swell painfully.

KS can cause serious problems or even become life threatening when the lesions are in the lungs, liver, or digestive tract. KS in the digestive tract, for example, can cause bleeding, while tumors in the lungs may cause trouble breathing.

Types of Kaposi sarcoma

There are four different types of KS defined by the different populations it develops in, but the changes within the KS cells are very similar.

Epidemic (AIDS-associated) Kaposi sarcoma

The most common type of KS in the United States is epidemic or AIDS-associated  KS. This type of KS develops in people who are infected with HIV, the virus that causes AIDS.

HIV stands for human immunodeficiency virus. A person infected with HIV (someone who is HIV-positive) does not necessarily have AIDS, but the virus can be present in the body for a long time, often many years, before causing major illness. The disease known as AIDS begins when the virus has seriously damaged a person's immune system, which means they can get certain types of infections (such as Kaposi sarcoma--associated herpesvirus, KSHV) or other medical complications, including KS.

KS is considered an AIDS defining illness. This means that when KS occurs in someone infected with HIV, that person officially has AIDS (and is not just HIV-positive).

In the United States, treating HIV infection with highly active antiretroviral therapy (HAART) has resulted in fewer cases of AIDS-associated KS. Still, some patients can develop KS in the first few months of HAART treatment.

For most patients with HIV, HAART can often keep advanced KS from developing. Still, KS can occur in people whose HIV is well controlled with HAART. Even if KS develops, it is still important to continue HAART.

In areas of the world where it is not easy to get HAART, KS in AIDS patients can advance quickly.

Classic (Mediterranean) Kaposi sarcoma

Classic KS occurs mainly in older people of Mediterranean, Eastern European, and Middle Eastern heritage. Classic KS is more common in men than in women. People typically have one or more lesions on the legs, ankles, or the soles of their feet. Compared to other types of KS, the lesions in this type do not grow as quickly, and new lesions do not develop as often. The immune system of people with classic KS is not as weak as it is in those who have epidemic KS, but it may be weaker than normal. Getting older can naturally weaken the immune system a little. When this occurs, people who already have a KSHV (Kaposi sarcoma--associated herpesvirus) infection are more likely to develop KS.

Endemic (African) Kaposi sarcoma

Endemic KS occurs in people living in Equatorial Africa and is sometimes called African KS. Kaposi sarcoma--associated herpesvirus (KSHV) infection is much more common in Africa than in other parts of the world, so the risk of KS is higher. Other factors in Africa that weaken the immune system (such as malaria, other chronic infections, and malnutrition) also probably contribute to the development of KS, since the disease affects a broader group of people that includes children and women. Endemic KS tends to occur in younger people (usually under age 40). Rarely a more aggressive form of endemic KS is seen in children before puberty. This type usually affects lymph nodes and other organs and can progress quickly.

Endemic KS used to be the most common type of KS in Africa. Then, as AIDS became more common in Africa, the epidemic type became more common.

Iatrogenic (transplant-related) Kaposi sarcoma

When KS develops in people whose immune systems have been suppressed after an organ transplant, it is called iatrogenic, or transplant-related KS. Most transplant patients need to take drugs to keep their immune system from rejecting (attacking) the new organ. But by weakening the body’s immune system, these drugs increase the chance that someone infected with KSHV (Kaposi sarcoma--associated herpesvirus) will develop KS. Stopping the immune-suppressing drugs or lowering their dose often makes KS lesions go away or get smaller.