Taken together, this study demonstrated that miR-21 may play an oncogenic role in DLBCL by comprehensively regulating the PI3K/AKT/mTOR/FOXO1 pathway (Fig. 4) and that a high miR-21 is associated with a poor prognosis for DLBCL patients. Here, FOXO1 is linked to diffuse large B-cell lymphoma.