SPP1 and lung adenocarcinoma: Metformin exerted antitumor activities in part by regulating the AFAP1-AS1/miR-3163/secreted phosphoprotein 1 (SPP1) axis in lung adenocarcinoma, and miR-316 overexpression caused suppression of PI3K/AKT/mTOR signaling, which could be re-activated by SPP1 overexpression [49].