Immunohistochemistry staining of xenografts derived from PTEN-knockout SMMC-7721 cells expressing PTENα-3F with an anti-Flag antibody not only detected positive staining in the tumor tissues, but also in the mouse-derived stroma, indicating that PTENα-3F is secreted by tumor cells into the extracellular space (Fig. 2A). This evidence concerns the gene PTEN and neoplasm.