Recent studies have found that NRG1 can be expressed in pituitary gonadotrophin cells and phosphorylatively activate the prolactotroph surface receptors to promote the release of prolactin in a juxtacrine manner (Zhao and Ren, 2011a, b; Zhao et al., 2011); and in vitro, NRG1 can also promote the invasion of breast cancer cells, regulate the actin cytoskeleton, and promote cancer cell metastasis in both autocrine or paracrine manners (Hijazi et al., 2000; Miller et al., 2006). Here, NRG1 is linked to breast cancer.