Moreover, in vitro studies demonstrated that neurotrophic factors secreted by reactive astrocytes such as IL-6, transforming growth factor-β (TGF-β), insulin-like growth factor-1 (IGF-1), and chemokine ligand 12a (CXCL12a) may contribute to the development of brain metastasis from breast cancer [18, 19]. This evidence concerns the gene IGF1 and breast cancer.