Fig. 1.

Relationship between ROS production and cancer cell development. Initiation, the first step among three stages in cancer, maintains the homeostasis of ROS against imbalance of ROS and regulates protein kinases, which have diverse cellular functions. Promotion, the second step, is related to DNA damage and induction of mutations appearing in the cellular signaling pathway. Progression, the third step, appears to activate EMT-related genes and other intracellular signaling pathway markers. Therefore, the generation of ROS is crucial to the three developmental stages of cancer; initiation, promotion, and progression.