Kaposi sarcoma is caused by a virus called the Kaposi sarcoma herpesvirus (KSHV), also known as human herpesvirus 8 (HHV8). KSHV belongs to the herpesvirus family. This virus is similar to Epstein-Barr virus, the virus that causes infectious mononucleosis ("mono") and contributes to several types of cancer. KSHV has to be present in the tumor cells of Kaposi sarcoma for it to develop. Endothelial cells, which are cells that line blood and lymphatic vessels, are infected with KSHV in KS. Scientists do not yet completely understand how KSHV causes KS, but they do know that the virus brings genetic material into the cells. These genes cause the cells to divide too much and to grow into nearby tissues.

KSHV infection is much more common than KS, and most people infected with this virus do not get KS. The percentage of people infected with KSHV is different in different places around the world. In the United States, studies have found that between 5% and 25% of people are infected with KSHV. The infection rate varies in different parts of the country. KSHV is more common in men who have sex with men than in men who only have sex with women.

In some areas of Africa, more than 90 % of the population shows signs of KSHV infection. In these areas the virus seems to spread from mother to child. KSHV is more commonly detected in saliva than in other body fluids. Many people infected with KSHV will never show any symptoms. A very small number of those infected will get a mild type of KS. In people whose immune systems are weakened (by AIDS, for example) infection with KSHV is much more likely to lead to KS.

Last Medical Review: 09/17/2009
Last Revised: 09/17/2009