We identified IDH1 <sup>R132H</sup> , PIK3CA <sup>E545K</sup> , <i>Cic</i> <sup>KO</sup> , <i>Fubp1</i> <sup>KO</sup> and <i>Cdkn2a</i> <sup>KO</sup> as the optimal combination (termed Oligo <sup>Cdkn2a</sup> ) to drive fully penetrant tumors that histologically resemble human grade II/III IDH-mutant, 1p/19q-codeleted oligodendroglioma. This evidence concerns the gene PIK3CA and oligodendroglioma.