TP53 and colitis: While Okada and colleagues observed that the functional importance of a positive feedback loop between p53 and miR-34a in tumor suppression could be solely evident in vivo upon p53-haploinsufficiency (only miR-34a ablation along with p53 heterozygosity significantly promoted oncogenesis in a mouse model of lung adenocarcinomas), Rokavec and collaborators showed that the sole Mir34a deletion was sufficient to enhance tumor invasion in a colitis-associated intestinal cancer mouse model, thus providing the first genetic evidence of a tumor suppressor function for miR-34a [27, 61].