Cyclin A2 belongs to the family of cyclins whose members regulate cell cycle progression by interacting with cyclin dependent kinases. It is essential for the control of the cell cycle at the G1/S (start) and the G2/M (mitosis) transitions. Increased expression of cyclin A2 has been observed in many types of cancer such as breast, cervix, liver, and lung. While it is not clear whether increased expression of cyclin A2 is a cause or result of tumorigenesis, it is indicative of prognostic values such as predictions of survival or relapse. Overexpression of cyclin A2 in mammalian cells can result in the delayed onset of metaphase and anaphase. It is also possible that cyclin A2-CDK contributes to tumorigenesis by the phosphorylation of oncoproteins or tumor suppressors like p53.