miR-21 differentially responding to exercise in circulation is well-known oncomiR that affects tumor-developing pathways such as sustained proliferation through PTEN (Phosphatase and Tensin Homolog), Sprouty, PI3K (Phosphoinositide 3-Kinase), PDCD4 (Programmed Cell Death Protein 4), impaired apoptosis through BTG2 (B-cell Translocation Gene 2), FasL (Pro-apoptic FAS Ligand), FBXO11 (F-box Protein 11), and TIMP3 (Tissue Inhibitor of Metalloproteinases 3) [107]. This evidence concerns the gene PDCD4 and neoplasm.