New insights into germ cell tumor formation.

Recent years have witnessed a number of new findings with significant implications for our understanding of the development of germ cell tumors. This communication reviews some of these recent insights with an emphasis on mechanisms that may convert a germ cell into a tumor cell. Three aspects are discussed in this review: (1) the early origin of germ cell tumors from primordial germ cells through an aberrant mitosis-to-meiosis switch; (2) errors during meiosis, which promote tumorigenic transformation of germ cells; and (3) the role of small RNAs such as oncomirs (miRNAs) and oncopirs (piRNAs) in germ cell tumor formation. Since much has been learned using a variety of organismal models, data obtained in experiments with mice, nematodes, fruit flies, and human data will be considered. Only exemplary references are included.