Fig. 1.

The positive and negative effects of reactive oxygen species (ROS) on tumor growth. On the anti-tumorigenic side of the balance: ROS induce the killing of microorganisms, apoptosis of tumor cells and the release of hypochlorous acid (HOCL) which directly promote tumor cytotoxicity. On the other pro-tumorigenic side of the balance: ROS induces DNA damage, genotoxicity, mediate T cell suppression as well as T cell tolerance, leading to the initiation of tumor growth. The delicate balance between ROS production and oxidative stress can modulate the pro- or anti-tumorigenic tumor microenvironment.