Review: In vivo models for defining molecular subtypes of the primitive neuroectodermal tumor genome: current challenges and solutions.

Primitive neuroectodermal tumors (PNET) of the brain include medulloblastoma (MB) and central nervous system primitive neuroectodermal tumor (CNS PNET) subtypes, which share histological features yet differ at the genomic level and in clinical outcome. Delineation of the genetic anomalies between PNET subtypes is a current challenge for establishing effective targeted therapeutic strategies against these aggressive tumors. Current efforts have demonstrated that specific molecular pathways drive a subset of MB and CNS PNET, but the genetic basis for the deadliest forms of these tumors remains poorly understood and anecdotal. This is in part due to an overall lack of biologically relevant in vivo and in vitro model systems capable of direct comparison and identification of the genetic origins among PNET subtypes. Forward genetic, random mutagenesis in mice is an effective phenotype-driven method to model the genetic origins of human disease including cancer. We have applied this method to PNET by developing a single Sleeping Beauty transposon insertional mutagenesis mouse model that recapitulates the morphological similarities and genetic heterogeneity of MB and CNS PNET capable of identifying genetic drivers important for genesis of PNET. Importantly, this model has allowed new PNET phenotypes to be observed and is designed to reveal biologically relevant candidate oncogenes and tumor suppressor genes for MB and CNS PNET molecular subgroups in mice and humans. The ultimate goal of the approach we have taken is to uncover new understanding of the genetic basis for MB and CNS PNET development, how they are distinguished from each other, and offer potential targets for therapeutic testing to improve patient clinical outcome.