E2F1 and neoplasm: Signaling pathways in antitumor mechanisms are involved in tumor initiation and progression correlating with biological aggressiveness: TP53 (tumor protein p53), RB1/INK4/ARF (retinoblastoma-associated protein 1/infestin 4/alternate open reading frame) and NOTCH1 (neurogenic locus homolog protein 1) signaling pathways are recognized.