Causes of Kaposi Sarcoma
Kaposi sarcoma is always caused by an infection with a virus called human herpesvirus 8, which is also known as Kaposi sarcoma-associated herpesvirus (KSHV). The virus, which is in the same family as Epstein-Barr virus, is rare in the United States. In fact, less than 1 percent of the general U.S. population is a carrier. The virus and the tumor are much more common in some other parts of the world.

How the virus is initially acquired and spread is poorly understood, but scientists have identified four distinct populations that represent nearly all cases of the disease. There is some evidence within those populations as to how KSHV is acquired and what causes some carriers to develop Kaposi sarcoma.

What are the risk factors for Kaposi sarcoma?
You must already be infected with Kaposi sarcoma-associated herpesvirus (KSHV) to develop Kaposi sarcoma. However, most people who have the virus will never get Kaposi sarcoma. The cancer is usually triggered by a weakened immune system in people who are HIV-positive, who have received an organ transplant or whose immune systems are weakened for other reasons, including age.