Ahamed et al. prepared spherical iron oxide nanoparticles with a smooth surface and an average diameter of 23 nm, which could induce the reactive oxygen species generation in HepG2 and A549 cancer cells, upregulating tumor suppressor gene p53 and caspase-3 and caspase-9 apoptotic genes to trigger cancer cells apoptosis (Ahamed et al., 2013). This evidence concerns the gene CASP9 and cancer.