Previous studies have reported a functional redundancy among the four members of the mammalian Id family, in particular Id1 and Id3 (referred to collectively here as Id), and their overlapping expression patterns during normal development and cancer (Lyden et al., 1999; Gupta et al., 2007; Anido et al., 2010; O'Brien et al., 2012; Niola et al., 2013). This evidence concerns the gene ID1 and cancer.