The level of Kaposi's sarcoma-associated herpesvirus (KSHV) cellular viremia in patients with Kaposi's sarcoma could be related to both the tumor burden and its progression. The origin of the spindle cell, the hallmark cell of Kaposi's sarcoma, is still debated. Two hypotheses may be formulated, favoring a lymphatic endothelial cell or an endothelial-cell precursor evolving into a lymphatic phenotype, both preferentially targeted by KSHV.