PTEN and gastric cancer: Exosomal miR-552-5p derived from a human gastric cancer cell line (SGC-7901) facilitated the malignant transformation of gastric epithelium (GES-1) and gastric adenocarcinoma (AGS) cells, and the effects were associated with inhibition of the synergy between the tumor suppressor “transducer of ERBB2.1” (TOB1) and PTEN.