PTEN and glioma: Histological analysis showed that control Pten−/−; Ink4a/arf−/− astrocytes yielded no intracranial tumors in 12 total animals tested, whereas RIOK2overexpresion; Pten−/−; Ink4a/arf−/− astrocytes formed invasive high-grade glial tumors composed of invasive spindle-shaped cells in 7 out of 10 total animals tested (p<.001 by chi-squared test) (Figure 4A, 4B).