E2F1 and cancer: E2F transcription factor 1 (E2F1) belongs to the E2F family of transcription factors, which plays key roles in regulating cell cycle, differentiation, and apoptosis in a variety of human cancers due to its abnormal overexpression as well as its interactions with effect factors including Bax, Cyclin D1, CDK4, PUMA, and so on [11, 12].