The patient went on to have a resection. 

Histology

Sections show mildly to moderately hypercellular fragments of brain tissue infiltrated by tumor cells with optically clear cytoplasm and centrally located round to ovoid nuclei with evenly distributed chromatin. Infiltrative growth including neuronal satellitosis is seen. There is no microvascular proliferation or palisading necrosis. Mitoses are rare.

Immunohistochemistry:

• GFAP Positive
• IDH-1 R132H Positive (mutated)
• ATRX Positive (not mutated)
• p53 Mosaic pattern (probably not mutated)
• p16 CDKN2A Mosaic pattern (probably not mutated)
• Ki67 labeling index: Approximately 5%

Mollecular markers:

• 1p/19q codeletion: DETECTED
• EGFR amplification: Not detected
• IDH1 codon 132: PATHOGENIC VARIANT DETECTED (R132H)
• IDH2 codon 172: No pathogenic variant detected
• BRAF codon 600: No pathogenic variant detected
• H3F3A codons 27 and 34: No pathogenic variant detected
• TERT promoter Chr5:1295228 (C228T) and chr5:1295250 (C250T): PATHOGENIC VARIANT DETECTED (C228T)

FINAL DIAGNOSIS: Oligodendroglioma, IDH-mutated and 1p/19q-codeleted (WHO grade II).