CCNE1 and cancer: Oncogenic activation of Cyclin E/CDK2 complex is frequently observed in human cancers and may be achieved by different genetic events, such as amplification of Cyclin E genes (CCNE1 or CCNE2), disruption of the RB/E2F pathway (leading to increased Cyclin E transcription), and mutation of FBXW7 ubiquitin ligase (causing accumulation of Cyclin E protein).