NF1 and pilocytic astrocytoma: Global prevalence of NF1 is about 1 in 3500.[1] Low-grade gliomas such as pilocytic astrocytomas and optic glioma are the majority of central nervous system neoplasms found in patients with NF1.[2] Glioblastoma (GBM) is the most lethal and common malignant brain tumor but rare in patients with NF1.