TGFB1 and cancer: Other putative mechanisms inducing senescence in primary and cancer stem cells include DNA damage by chemotherapeutics [37], hypoxia [58], oncogene activation (oncogenic β-catenin) [36], and the dysregulation of microenvironmental growth factors such as TGF-β (transforming growth factor beta) or BMP7 (bone morphogenetic protein 7) [59,60].