CTCF is absolutely required for development as Ctcf null mouse embyros fail to develop into blastocysts.42 Thus we expect complete loss of CTCF in tumours would be detrimental to cell viability and tumourigenesis, similar to when enforced deletion of both alleles of DICER1, a known haploinsufficient tumour suppressor gene, leads to inhibition of tumourigenesis.43 This evidence concerns the gene DICER1 and neoplasm.