For instance, upon binding with their receptors, EGF or IGF subsequently activates mitogen activated protein kinase (MAPK), which in turn phosphorylates Ser118 in the activation function-1 (AF-1) domain of ERα, resulting in the conformation change and translocation of ERα, transcription of target genes and proliferation of breast cancer cells [28]. The gene discussed is ESR1; the disease is breast cancer.