CDK1 and breast cancer: Cyclin B/CDK1 complex keeps inactive until it is activated by the Cdc25 phosphatase family in prophase, which plays an important role in G2-M phase transition.[9,12–14] Overexpression of cyclin B has proved to drive tumorigenesis in many tumors, including breast cancer.[15,16] Many studies have evaluated the relationship between the expression of cyclin B and survival in breast cancer patients.