At low to moderate levels, ROS stimulates mitogen-activated protein kinase (MAPK) phosphorylation, cyclin D1 expression and c-Jun N-terminal kinase (JNK) activation, all of which are linked to cancer cell growth and survival16, and also induces mutagenesis by formation of 8-oxoguanine, which can lead to G-T or G-A transversion17. The gene discussed is CCND1; the disease is cancer.