E2F1 and neoplasm: Serving as tumor-suppressive miRNA, exosomal miR-17/20 blocks irregular cell-cycle by silencing E2F transcription factor 1 (E2F1) expression, as well as causes alteration in the secretion of a series of pro-metastatic cytokines, such as C-X-C motif chemokine ligand 1 (CXCL1), cytokeratin 8 (CK8), and Interleukin-8 (IL-8).