ID1 and glioblastoma: RNA interference technology for knocking down Id expression is broadly used in cancer research (e.g., siRNA targeting Id1 reduces glioblastoma cell invasion and self-renewal (Soroceanu et al. 2013), and implantation of Id2-shRNA knockdown neuroblastoma cells into mice attenuates tumorigenicity, renders the cells immunogenic, and induces host immunity (Chakrabarti et al. 2015)).