FBXW7 and neoplasm: This discrepancy may be a mouse-specific phenomenon resulting from a decreased requirement for ‘second hits’ at Fbxw7 compared with humans,38 as our in vitro data suggest; or it may reflect the fact that heterozygous null human FBXW7 genotypes do have some, submaximal, tumour promoting effects, perhaps in a continuum fashion.39 Overall, our data support the notion that FBXW7 is not a classical tumour suppressor gene.