Abstract
BACKGROUND: High grade astrocytoma with piloid features (HGAP) is a newly recognized tumor with a distinct DNA methylation profile. Its clinical course, treatment response, and outcomes remain poorly understood. METHODS: We conducted a retrospective cohort study across three Mayo Clinic sites including adults with a HGAP diagnosis confirmed by DNA methylation profiling. RESULTS: 17 patients were included (median age 38 years, Q1, Q3: 29–59; 9 male). DNA methylation-based tumor classification using the NCI/Bethesda classifier (v2) indicated a match to HGAP with high confidence (calibrated score >0.9) in 14 cases and was suggestive in 3 cases. All had MAPK pathway alterations (NF-1 mutation in 11, FGFR1 mutation in 2, KIAA1549::BRAF fusion in 2, FGFR1 transcript variant suggestive of internal tandem duplication in 1, KANK2::NTRK2 fusion in 1). All tumors also had CDKN2A/B homozygous deletion and 9 lost ATRX expression. Tumors were infratentorial (n=8), supratentorial (n=7), and spinal (n=2) at initial presentation. First line treatment included surgery followed by chemoradiation with temozolomide (n=12), surgery followed by radiation (n=4), radiation alone (n=1), and surgery alone (n=1). Gross total resection was achieved in 3/17, 8/17 had subtotal resection and 5/17 had biopsy. 14/17 received a median RT dose of 5700 cGy (range, 4005–6000) in 30 fractions. The median follow-up duration was 34.9 months. 8 patients experienced disease progression. The median progression-free survival (mPFS) was 30.3 months (95% CI: 15.4–NR). 6/8 underwent surgery; 3/8 underwent RT. Systemic therapies were administered in 5/8 (lomustine, bevacizumab, pembrolizumab, temozolomide, trametinib, tovorafenib). 3/17 patients died due to progressive disease with an OS of 54.2, 94.6 and 17.4 months, respectively. The mOS for the whole cohort was 54.2 months (95% CI: 54.2-NR). CONCLUSION: While the optimal management of this newly recognized entity has yet to be established, our cohort demonstrates a clinical behavior consistent with CNS WHO grade 3, aligning with current WHO interpretations.