Syljuasen et al. [44] have proved that in human osteosarcoma cells, a G2 checkpoint arrest occurs, induced by exposure to ionizing radiation, correlated with DNA breaks (measured by gamma H2AX assay); however, the cells are able to exit this temporary arrest and undergo mitosis at around 30h from radiation treatment, while still expressing the markers for unrepaired DNA double-strand breaks. Here, H2AX is linked to osteosarcoma.