FES and cancer: The original identification of FES as a retroviral oncogene underscores its potential role in cancer; however, understanding of its function has been complicated by subsequent research that has implicated FES in both tumor-promotive and tumor-suppressive roles (Bardelli et al. 2003; Delfino et al. 2006; Sangrar et al. 2005; Voisset et al. 2010; Zhang et al. 2011; Olvedy et al. 2017).