In this model, astrocytes with targeted deletion of neurofibromin Nf1−∕− are poised to be tumorigenic in the appropriate setting, which includes requirements for heterozygous loss of neurofibromin in tumor stromal elements and other, as yet to be fully defined factors, that stereotypically promote tumorigenesis in the optic nerves and optic chiasm. This evidence concerns the gene NF1 and neoplasm.