PCNA and Kaposi's sarcoma: Whether KSHV-infected endothelial cells in KS tumours in vivo actually proliferate at an increased rate has however not been clearly established: in one study only 20% of KS spindle cells stained positive for the cellular proliferation marker PCNA [235], while an increased staining for TP53 and Ki-67, another proliferation marker, was reported in advanced KS lesions by another group [236].