Fig. 1.

Schematic illustration of the BM program. A The most common BMs are from the lung, breast and melanoma, and less from the prostate, colorectum, kidney and other organs. B The process of MIC entry into the brain and BM colonization. C BM seizes the opportunity for survival in the brain due to the imbalance of the inflammatory response in two types of polarized brain cells. D BM fortress with immunosuppressive defenses and support from glial cells is finally formed. Created with BioRender.com. BM, brain metastases; MIC, metastases-initiating cell; CTC, circulating tumor cell; EMT, epithelial–mesenchymal transition; MET, mesenchymal–epithelial transition; EVs, extracellular vesicles; CXCL10, C-X-C motif chemokine 10