Figure 1

Pleiotropic effects of TGF β in the tumour microenvironment. Representation of a primary tumour with cancer stem cells (CSCs) or metastasis-initiating cells (light green) and the bulk of the tumour cells (orange). Different cell types surrounding the tumour mass can positively contribute to tumour progression, invasiveness and metastatic dissemination, acting on the tumour cells but also receiving input from the tumour cells (bi-directional arrows). Cells that can inhibit tumour progression are linked to the tumour mass with a negative arrow. The contributions of TGFβ and additional cytokines and chemokines are highlighted next to each arrow. As graphic simplification, haematogenous or lymphatic metastatic dissemination shows solely CSCs co-migrating with stromal cells and platelets. At the secondary site, metastatic colonisation and growth is shown; whether stromal cells dissociate from the metastasising clonal population or whether they are replaced by new local stromal cells is currently unknown (?).