NF1 and central nervous system cancer: The co-occurrence of cavernous malformations with both gliomas and tumors of Schwann cell origin may be explained by the fact that chromosome 7 monosomy and 7q22 deletions occur as common secondary events after hyperactivation of Ras oncogenes or mutation of the Ras-GAP protein neurofibromatosis-1 (NF-1) gene [68,69].