Id-2 has been shown to bind and inhibit the function of retinoblastoma protein, a tumour suppressor protein (Iavarone et al, 1994; Lasorella et al, 1996) and therefore has been implicated in tumour progression in several cancer types (Maruyama et al, 1999; Fukuma et al, 2003; Coppe et al, 2004). This evidence concerns the gene ID2 and neoplasm.