[miRNAs and cancer]

Contrary to current belief, the concept of microRNA (miRNA) is quite old. Indeed, the first report on a small RNA able to control the translation of a specific messenger RNA (and therefore called translational control RNA or tcRNA) dates 35-year back. miRNAs waited until 1993 to be "rediscovered" and become the focus of an intense research activity which led to the discovery of several hundreds of them, to the unraveling of their biosynthesis and of their involvement in numerous physiological and pathological processes, notably in cancer. They represent another testimony to the crucial role plaid by RNA at all levels of gene expression regulation and dysregulation. If the old saying "the roots of cancer lie in our DNA" is still valid, one cannot anymore overlook, as has been the case for too long, that its role is not limited to the univocal expression of protein-coding messengers but rather that many downstream mechanisms exist to control and eventually dramatically alter their expression qualitatively (though alternative splicing) as well as quantitatively thanks to the miRNAs which are the topic of this review.