TCF7L2 and type 2 diabetes mellitus: Several type 2 diabetes susceptibility genes are known to play a role in cancer development (e.g. TCF7L2, CDKN2A/B, AKT2, PPARG, PTEN and HNF1B) but the evidence is relatively scarce for shared genetic aetiology between type 2 diabetes predisposing alleles and the observationally associated cancers.