NRG1 and breast cancer: The astrocyte-derived secretion of the Erb-B2 receptor tyrosine kinase 3 (ErbB3, HER3) ligand neuregulin-1 (NRG-1) induces the proliferation, invasion, and BBB transmigration in Erb-B2 receptor tyrosine kinase 2 (ErbB2, HER2)-positive BC cells [114,115].