HGF and central nervous system cancer: HGF is primarily expressed and secreted by stromal cells such as cancer-associated fibroblasts (CAFs) and tumor-associated macrophages (TAMs) that surround malignant tumors, but it can also be released by various cancer cell types such as renal cell carcinoma, colorectal carcinoma, breast carcinoma, glioma, and multiple myeloma [26,27,28,29,30,31,32].