41. Impact of chromosome aberrations on tumor recurrence risk in grade I–II pilocytic astrocytoma

Brain tumors are the most common malignancy of childhood. Approximately 50% of pediatric CNS tumors are astrocytomas, most low grade. Low grade glioma (LGG) are WHO grade I or II tumors. Pilocytic astrocytoma (PA) is the most common; accounts for 33% of all gliomas in children 0–14 years and ∼18% of all childhood brain tumors. Prognosis with this slow-growing tumor is excellent; 10 year overall survival of ∼95%. However, event free survival averages ∼50%. Patient age and extent of tumor resection are key prognostic factors; tumor location and size impact resection and outcome. Histopathological features indicate PA is a benign tumor and rarely are anaplastic features of malignancy present. The study sought to identify chromosomal aberrations that correlate with increased risk of tumor recurrence. Observation shows that while the majority of PA have a normal karyotype, a portion have highly abnormal karyotypes. The clinical significance of these aberrant karyotypes remains unclear. Pathology archives were searched for PA between mid-2008 and mid-2017. Record review of 125 LGG included cytogenetic analysis, histopathology, tumor location, patient age, extent of surgical resection, chemotherapy, radiotherapy, and outcome (recurrent tumor). Karyotypes were classified as normal, hyperdiploid, tetraploid, aberrant, or simple. Karyotypes were “aberrant” if they had multiple bizarre chromosome abnormalities, had multiple telomeric associations or translocations, or had multiple dicentric chromosomes. Aberrant chromosomal findings that could not be attributed to tissue culture artifact were included in the clinical report. This study assessed the relationship of aberrant karyotypes with risk of tumor recurrence in these ‘benign’ tumors.