The Importance of Ki67 in Grading Meningiomas: A 20-Year Retrospective Study.

Abstract Context: The Ki67 proliferation index is a key marker for evaluating the proliferative activity of tumors. While valuable in assessing meningiomas, it has not yet been integrated as a primary grading criterion in the World Health Organization (WHO) classification systems. Design: This retrospective study analyzed 377 meningioma cases from a single institution over a 20-year period. Following the WHO 2021 criteria, 228 cases (60%) were classified as Grade 1, 134 cases (36%) as Grade 2, and 15 cases (4%) as Grade 3. Ki67 immunostaining was performed on all specimens, and the percentage of positive cells was recorded for each case. Results: The mean Ki67 scores for the different grades of meningiomas were as follows: 1.9% for Grade 1 (range: 0%-3.4%), 6.2% for Grade 2 (range: 3.6%-8.6%), and 22.8% for Grade 3 (range: 8.4%-32.5%). The differences in Ki67 scores across the grades were statistically significant (P<0.001). Figure A illustrates a Grade 1 meningioma with a very low Ki67 score of 0%, while Figure B presents a typical Grade 1 meningioma with a Ki67 score of 2%. Figure C displays a Grade 2 meningioma with a Ki67 score of 8%, and Figure D shows a significantly high Ki67 score of 22% for a Grade 3 meningioma. Conclusions: Our findings underscore the critical role of Ki67 in accurately determining the grade of meningiomas. The clear correlation between increasing Ki67 scores and higher tumor grades suggests that future classification systems should incorporate Ki67 as a formal grading criterion.