E2F1 and neoplasm: Previous studies showed that PTTG1 was directly regulated by estrogen, insulin, basic fibroblast growth factor, epidermal growth factor, β-catenin/transcription factor, Rb/E2F1 pathways, STAT3, etc., and consequently involved in multiple steps of tumor progression including tumorigenesis, invasiveness, metastasis, and angiogenesis [11, 20–24, 47].