They also showed that shedding of tumor DNA into the CSF was significantly associated with tumor progression, tumor burden, the spread of tumor toward the ventricular system and shorter median OS.37 Huang et al identified Histone H3 mutations (H3F3A and HIST1H3B) in ctDNA derived from CSF of children with diffuse midline gliomas with a sensitivity of 87.5% and specificity of 100%.38 Similarly, Pan et al identified H3F3A, HIST1H3B, TP53, ATRX, PDGFRA, FAT1, PPM1D, IDH1, NF1, PIK3CA, and ACVR1 mutations in ctDNA isolated from CSF of patients with brain stem gliomas (Table 1). The gene discussed is PIK3CA; the disease is neoplasm.