In the WHO classification of tumor grade, low-grade gliomas (WHO Grade II) have which proliferative marker value on Ki-67 (MIB-1) immunostaining that distinguishes them from Grade III (anaplastic)?
- A Ki-67 index less than 5–6% ✓
- B Ki-67 index less than 1%
- C Ki-67 index less than 15%
- D Ki-67 index less than 25%
Correct answer: A. Ki-67 index less than 5–6%
Explanation
In the 2021 WHO Classification of CNS Tumors, low-grade (Grade 2) gliomas typically show Ki-67/MIB-1 proliferation indices below 5–6%, whereas Grade 3 (anaplastic) tumors show indices of 5–15% or higher. Ki-67 is used as a supportive — not standalone — criterion alongside mitotic index, necrosis, and vascular proliferation. Grade 4 (glioblastoma) typically shows Ki-67 >20%. This distinction is particularly relevant for surgical decision-making regarding extent of resection and adjuvant treatment.
Reference: Bailey & Love's Short Practice of Surgery, 27th ed.
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