ID1 and cancer: The stemcell niche environment is rich in other growth factors, such as fibroblast growth factor-2 (FGF-2) and epidermal growth factor (EGF), that induce Id expression through the ERK–MEK pathway in cancer cells by direct binding of early growth responsive protein 1 (Egr-1) to the Id promoter (Borlak et al. 2005; Passiatore et al. 2011; Tournay and Benezra 1996).