In 1872, Moritz Kaposi (1837–1902), a Hungarian dermatologist, described five male patients presenting with deep red to brown-violet plaques or nodules on the skin of the lower extremities (Figure 159.1; for color reproduction, see Color Plate 159.1) (1). This disease, later designated Kaposi's Sarcoma (KS), was uniformly fatal for his patients. Kaposi stated: “The disease must, from our present experience, be considered from the onset not only as incurable, but also as deadly.”

Today, KS is recognized as the most common tumor in human immunodeficiency virus (HIV)–1 infected individuals. The tumors are multifocal, highly vascularized neoplasms characterized histologically by spindle-shaped tumor cells that formslit-like vascular spaces often filledwith erythrocytes (see Figure 159.1). The lesions also contain fibroblasts, endothelial cells (ECs, indicating angiogenesis), and an inflammatory infiltrate consisting of lymphocytes, eosinophils, and plasma cells. Early lesions resemble granulation tissue and, as the disease progresses, the tumor cells coalesce to formlarge masses. In these late-stage lesions, a vast majority of the tumor cells, as well as some surrounding ECs, are infected with the KSassociated herpesvirus (KSHV, also known as human herpesvirus [HHV]–8). This virus, which is believed to be the etiologic agent responsible for KS, is discussed in this chapter. As noted by Kaposi, the extremities are initially involved in most cases; however, the disease can progress to involve virtually any internal organ, particularly the lungs and gastrointestinal tract. Curative therapy has not been developed for KS, and current treatments are only able to temporarily relieve its symptoms (2).

THE KAPOSI'S SARCOMA-ASSOCIATED HERPESVIRUS

Research in KS changed dramatically in 1994, when Chang, Moore, and colleagues identified novel herpesvirus-like DNA sequences in over 90% of KS lesions (3).