TGFB1 and breast cancer: The secretory growth factor Bone morphogenetic proteins of the TGF-β family was co-injected into a xeno-transplanted zebrafish model; Grem1, a Bone morphogenetic proteins antagonist produced by CAFs, was found to promote the activation of fibroblasts and infiltration and extravasation of breast cancer cells, thus, promoting the formation of Micrometastases.