APC and cancer: Several studies have proposed that Fbxw7 acts in a haploinsufficient manner in cancers and there is some evidence for this possibility: heterozygous null Fbxw7 mutants have a greater susceptibility to radiation-induced tumourigenesis 2 and enhance intestinal tumourigenesis in an Apc-mutant background (although not when Fbxw7 alone is mutated) 4.