Early progressive disease in IDH-mutant grade 2 and 3 astrocytoma without CDKN2A/B homozygous deletions may indicate radiation necrosis

Purpose Isocitrate dehydrogenase (IDH)-mutant astrocytoma without cyclin-dependent kinase inhibitor 2A/B ( CDKN2A/B ) homozygous deletion (HD) typically follows a slow clinical course. However, some cases show early progression on MRI, and these characteristics have not been fully reported. This study aimed to elucidate the characteristics of those cases. Methods This retrospective study included 52 primary cases with astrocytoma, IDH-mutant, CNS WHO grade 2–3, reclassified from the original diagnosis based on WHO2021 classification. Patients underwent surgery followed by radiation therapy or/and chemotherapy at our institution from 2006 to 2019. Progression-free survival (PFS) and overall survival (OS) was analyzed. Results The grade 2 and 3 astrocytomas were 24 and 28, respectively; the median age was 38 years. Forty-three patients underwent radiotherapy, with or without chemotherapy. Progression was diagnosed in 28 patients through MRI, and early progression within 2 years of initial radiotherapy occurred in 11 cases (21.2%). Histologically, radiation necrosis was confirmed in four out of these 11 patients (36.4%). Two patients with telomerase reverse transcriptase ( TERT ) promoter mutations experienced recurrence within three years of the initial surgery. The 2-year true progression-free, except radiation necrosis, at 2 years after surgery in astrocytoma grades 2 and 3 was 91.3% in grade 2 and 88.5% in grade 3 astrocytoma. Conclusion The possibility of radiation necrosis exists in the early progression of grade 2–3 astrocytoma. A second surgery should be performed to confirm true recurrence or radiation necrosis. Astrocytomas with TERT promoter mutations may relapse relatively early and should be followed up with caution.