Kaposi's sarcoma (KS) was described as a clinical marker in some of the first identified cases of acquired immunodeficiency syndrome (AIDS) in the USA, and remains the most common tumor associated with human immunodeficiency virus (HIV) infection. The KS lesion contains several cell types, including spindle and endothelial, which express surface markers consistent with vascular, lymphatic or smooth muscle lineages. The growth characteristics of KS in vivo and in vitro are influenced by an array of cytokines, growth factors, and viral gene products, especially in an underlying immunosuppression, suggesting that it is more a reactive tumor than a typical malignancy. Epidemiological analysis strongly suggests that AIDS-associated KS is caused by a sexually-transmitted agent in concert with HIV. The epidemiology and pathogenesis of KS is reviewed, focusing on the two major explanations of KS etiology: alterations in growth factor circuits and infection with non-HIV viruses.

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