TP53 and lung carcinoma: For example, the miR-17-miR-92 cluster in T-cell acute lymphoblastic leukemia reduces the level of the transcription factor E2F1[5], [6]; miR-21 down-regulates the tumor-inhibiting factor PTEN in lung cancer cells; and miR-125b is an important repressor of p53 and inhibits p53-induced apoptosis in human neuroblastoma cells [7].