Kaposi sarcoma (KS) is a cancer that develops from the cells that line lymph or blood vessels. KS is caused by the Kaposi sarcoma herpesvirus (KSHV), which is also called human herpesvirus 8. Although people do not develop KS without first getting infected with KSHV, most people who are infected with KSHV never develop KS. Someone who is infected with KSHV is more likely to develop KS if their immune system doesn’t work properly. The most common immune system problem that contributes to KS is infection with the human immunodeficiency virus (HIV).

The abnormal cells of KS form purple, red, or brown blotches or tumors on the skin. These affected areas are called lesions. Although the skin lesions of KS may look bad, in many cases, the lesions cause no symptoms. In other cases, the disease causes painful swelling, especially in the legs, groin area, or skin around the eyes. 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 difficulty breathing.

Types of Kaposi sarcoma

Some cancers such as lung cancer or breast cancer have several different types that indicate either different types of cells have become cancerous or different types of changes have occurred within a particular cell type. On the other hand, the different types of KS are defined by the different populations it develops in, but the changes within the KS cells are very similar.

Epidemic (AIDS-related) Kaposi sarcoma

The most common type of Kaposi sarcoma (KS) in the United States is epidemic or AIDS-related KS. This type of KS develops in people who are infected with HIV, the virus that causes AIDS. A person infected with HIV (that is, who is HIV-positive) does not necessarily have AIDS. The virus can be present in the body for a long time, typically many years, before causing major illness. The disease known as AIDS begins when the virus has seriously damaged the immune system, which results in certain types of infections and other medical complications. When HIV damages the immune system, people who also are infected with Kaposi sarcoma herpesvirus are more likely to develop KS.

Treatment of HIV infection with highly active antiretroviral therapy (HAART) has decreased the incidence of epidemic KS and can often keep advanced KS from developing. Not everyone whose HIV is well controlled is protected from KS, and sometimes aggressive KS develops that requires the use of chemotherapy or other treatments. In areas of the world where HAART is not easy to obtain, KS in AIDS patients can advance quickly and cause death in just 6 months.

Classic (Mediterranean) Kaposi sarcoma

Classic Kaposi sarcoma (KS) occurs in elderly people of Mediterranean, Eastern European, and Middle Eastern heritage. Classic KS is more common in men than in women. Patients typically have one or more lesions on the legs, ankles, or the soles of the feet. In comparison with other types of KS, the lesions in this type do not grow as quickly, and new lesions do not develop as often. The people who get classic KS come from areas where KS herpesvirus infection is more common than in the US or Northern Europe. The immune system of people with classic KS is not as weakened as those who have epidemic KS. But, getting older may naturally weaken their immunity a little, which makes people more likely to develop KS if they already have a KS herpesvirus infection.

Endemic (African) Kaposi sarcoma

Endemic Kaposi sarcoma (KS) occurs in people living in Equatorial Africa and is sometimes called African KS. KS herpesvirus infection is much more common in Africa than in other parts of the world, increasing the chance of KS developing. There appear to be other factors in Africa that 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 the lymph nodes and other organs and can lead to death within a year.

Iatrogenic (transplant associated) Kaposi sarcoma

When Kaposi sarcoma (KS) develops in people whose immune systems have been suppressed after an organ transplant it is called iatrogenic, or transplant-associated, KS. Most transplant patients take drugs to keep the immune system from rejecting (attacking and killing) the new organ. These drugs weaken the body's defenses, and this increases the likelihood that people infected with KSHV will develop KS. Stopping the immune suppressing drugs or lowering their dose often makes KS lesions disappear or get smaller.