PTEN and oligoastrocytoma: The simultaneous occurrence of alterations in two genes was observed as follows: PTEN and CDKN2A genes, identified in nine patients, 8/46 (17.4%) astrocytomas, and 1/4 (25%) oligoastrocytoma; TP53 and CDKN2A genes, identified in 5/46 (10.9%) astrocytomas; and TP53 and PTEN genes, identified in 1/46 (2.2%) astrocytomas.