Non-senescent osteosarcoma U2OS cells stably transfected with green fluorescent protein (GFP) were mixed with drug-induced senescent U2OS cells (prepared by exposure to 10 μM BrdU and 10 μM DMA as previously described [24]) at a ratio 10:1, cultured together for 24 hours and then assessed for the presence of GFP and serine 139 phosphorylated histone H2AX (γH2AX) foci as a marker of formation of DNA DSBs [51, 52]. The gene discussed is H2AX; the disease is osteosarcoma.