Pilocytic astrocytoma (PA) is the most common glioma in the pediatric population. PAs can
exhibit variable behavior that does not always cor relate with location, yet at present there is
no way to predict which tumors will be more aggressive. To address this problem, an
institutional cohort of 147 PAs (118 with outcome data) from both cerebellar and noncer-
ebellar locations (spine, diencephalon, midbrain, brainstem and cortex) was utilized.
Parameters included quanti?cation of characteristic mor phologic variables as well as genes
previously shown to be of relevance in high-grade gliomas, including MIB-1, p53 and
MGMT. In this cohort, the classic biphasic appearance was most common in cerebellar
tumors, whereas noncerebellar tumors were predominantly microcystic. Associations with
outcome suggest that the presence of degenerative atypia may be a favorable factor in PAs.
Oligodendroglial mor phology and the absence of leptomeningeal invasion are adverse
histologic factors, but only in cerebellar tumors. Conversely, MIB-1 proliferation index and
p53 and MGMT expression do not cor relate with outcome. Mor phologic biomarkers thus do
exist for PAs, but the utility of each biomarker varies according to location. These results
suggest that PAs differ fundamentally according to location; therefore, biological behavior
may not simply depend on extent of resection.