Intravital Imaging Illuminates Transforming Growth Factor β Signaling Switches during Metastasis

Transforming growth factor β (TGFβ) has seemingly contradictory roles in tumor progression: it can promote metastatic invasion but also act as a tumor suppressor. Recently, two studies have used intravital imaging to unravel the role of TGFβ at different stages of the metastatic process. TGFβ promotes single cell motility, which enables invasion into blood vessels. However the activation of TGFβ signaling is a transient event and is not maintained at distant sites. The downregulation of TGFβ signaling at secondary sites then permits growth of secondary tumors. In the absence of TGFβ, cells are restricted to collective movement and lymphatic spread. Here, we discuss these findings and their potential implications. Cancer Res; 70(9); 3435–9. ©2010 AACR.