*3.2.2 Breast cancer*

In breast cancer, the TGF network in liver metastasis can be explained by the ZEB1-miR-190-SMAD2 axis [124]. miR-1204 inhibits vitamin D receptors (VDR), which promotes epithelial-mesenchymal transition and metastasis [125]. As a ceRNA of miR-1299, circular RNA ciRS-7 promotes lung and liver metastases by targeting MMPs [126]. Wang et al. found circROBO1 was upregulated to boost tumor development and liver metastasis in vivo. Further research revealed the mechanism that circROBO1 upregulated KLF5 by sponging miR-217-5p, allowing KLF5 to activate FUS transcription, hence promoting circROBO1 back splicing [127].
