CDKN2A and pleomorphic xanthoastrocytoma: Since copy number of chromosome 9 increased despite CDKN2A deletion, addition studies (preferably in more than 1 models) are needed to examine if CDKN2A deletion is associated with the in vivo progression and in vitro growth of neurospheres, and if amplified chromosome 9 is involved in and/or drive tumor progression in PXA.