MTOR and diffuse large B-cell lymphoma: Studies of clinical DLBCL specimens have shown that upregulated miR-21 expression inhibits the expression of forkhead box protein O1 (FOXO1) and PTEN, thereby increasing the activity of the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT)/mammalian target of rapamycin (mTOR) signaling pathway and imparting more malignant biological characteristics to DLBCL cells.