However, there is increasing evidence for the functional non-equivalence of HIF-1α and HIF-2α, and in cancer, several recent studies have indicated that, at least in certain settings, they have contrasting effects on tumour growth (Maranchie et al, 2002; Kondo et al, 2002, 2003; Zimmer et al, 2004; Covello et al, 2005; Raval et al, 2005). This evidence concerns the gene HIF1A and neoplasm.