Rac1 is overexpressed in spindle cells from KS biopsies and expression of a constitutively active Rac1 (Ma et al., 2009) or RhoA (Martin et al., 2007) in transgenic mice causes the development of KS-like tumors, whereas inhibition of Rac1 (Montaner et al., 2004) or knockdown of RhoA expression (Martin et al., 2007) reduces ORF74 tumorogenesis in vivo. This evidence concerns the gene RHOA and Kaposi's sarcoma.