In this model, PDGF-B overexpression promotes oligodendrogliomas and oligoastrocytomas from neural progenitors and astrocytes, and the combination of activated Ras and Akt induces high-grade gliomas [1], while neither activated Ras nor Akt alone is sufficient to induce GBM formation [2]. The gene discussed is PDGFB; the disease is oligodendroglioma.