MYC and neoplasm: The downregulation of miRNA subsets implies a tumour-suppressor function, which is often observed in tumour development; for example, downregulated let-7 in lung cancer (Takamizawa et al, 2004; Johnson et al, 2005; Yanaihara et al, 2006) suppresses Ras (Johnson et al, 2005), deleted or downregulated miR-15 and miR-16 in chronic lymphocytic leukemia suppress BCL2 (Calin et al, 2002; Cimmino et al, 2005), and miR-17-5p and miR-20a control the balance of cell death and proliferation driven by the proto-oncogene c-Myc (O'Donnell et al, 2005).