Recent studies have indicated that miRNAs play an important role in cancer development. This concerted research effort aims to bring together the expertise within the Center for Medical Genetics in order to synergistically investigate the biology of miRNAs in cancer development. We will focus on deregultaed miRNA expression in selected pediatric malignancies, adult acute myeloid leukemia and breast cancer, focussing on the specifically implicated miRNAs, their prognostic significance and function in controlling signalling networks as targets for molecular therapy.