Epigen is a member of the EGF superfamily of proteins that signals through the ErbB receptor-1. As are other members of the EGF superfamily, human Epigen is initially synthesized as a glycosylated 14.7 kDa transmembrane-bound precursor that is proteolytically cleaved from the plasma membrane. Epigen is mitogenic for fibroblasts and epithelial cells. Although Epigen has low binding affinity to EGF receptors, it has strong mitogenic potency due to its prolonged binding presence. Expression of Epigen has been detected in multiple tissues including testis, liver and heart. Transcript and protein expression have also been reported in cancer specimens of the breast, bladder, and prostate.