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. The gene discussed is RAC1; the disease is Kaposi's sarcoma.