Heregulin, also named neuregulin-1 type I, is a family of growth factors that act as ligands for the epidermal growth factor receptors, including ERBB3 and ERBB4. Heregulins regulate survival, proliferation, and differentiation of the cells during development and wound healing. Heregulin-β1 is one of the Heregulin isoforms derived from alternative splicing. Binding of Heregulin-β1 to receptor tyrosine kinases ERBB3 or ERBB4 results in the recruitment and activation of ERBB2, subsequently transducing signaling cascades through the mitogen-activated protein kinase (MAPK) and phosphatidylinositol-3 kinase (PI3K) pathways. It has been suggested that heregulin-β1 participates in the tumorgenesis and metastasis of breast cancer, promoting proliferation, migration, and invasion of breast cancer cells.