PATH-79. High-grade astrocytoma with piloid features (HGAP) comprehensive update: histological grading, molecular markers and clinical outcomes

Abstract BACKGROUND HGAP was first described in 2018. However, prognostic factors of clinical outcome are not well-understood secondary to recent recognition and paucity of data for this diagnostic entity. Here, we utilize a large HGAP cohort (n=252) to survey the genomic landscape and explore prognostic correlates. METHODS NIH DNA methylation profiling was performed to identify HGAP cases and combined with publicly available datasets. Evaluable molecular markers, patient demographics, tumor location, imaging reports, treatment history (e.g. temozolomide, targeted therapy, surgery, and radiation) and survival data were assessed. Kaplan-Meier analysis was performed. RESULTS The cohort included cases that matched to HGAP on the NIH/Bethesda methylation classifier at ≥0.9 confidence score. More males (60%) than females (40%) were in the cohort. Twenty-one percent of patients were known to have neurofibromatosis type 1. Posterior fossa location was predominant (57%, n=131). Common genomic findings included alterations in NF1 (58%), ATRX (50%), FGFR1 (15%), TP53 (9%) and PIK3CA (8%). CDKN2A/B homozygous deletion was identified in 80% of cases. MGMT promoter methylation was found in 55% of cases. Median progression free survival (mPFS) was 24 months (mo), and median overall survival (mOS) was 108 mo. Central histological review revealed 67% of cases were high-grade. High-grade histopathology (brisk mitotic activity) was not associated with survival. Immunohistochemical ATRX loss was associated with shorter mPFS (18.0 mo vs 35.5 mo, p=0.04) and mOS (93.7 mo vs not reached, p=0.04). The presence of ATRX genetic alterations was associated with shorter mOS (30 mo vs not reached, p=0.008). CDKN2A/B homozygous deletion and MGMT status were not correlative with patient outcome. CONCLUSION HGAP is a glial neoplasm that shows frequent tumor recurrence. The majority of HGAP cases are high-grade. Our analysis of correlates with patient outcome suggests immunohistochemical ATRX loss and molecular ATRX alteration may be important poor prognostic markers.