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GEMM classification for meningiomas [59].
| Phenotype | Description |
|---|---|
| Meningothelial proliferation (early tumor formation) | Microscopic lesions composed of meningothelial cells |
| Grade I meningiomas | No mitotic figures, mild cytologic atypia, no brain invasion |
| Grade II meningiomas | One or two mitoses/HPF, true brain invasion |
| Grade III meningiomas | Marked cellular atypia (giant nuclei, pleomorphic nuclei, nuclei with marked chromatin clearing), brisk mitotic activity (three or more mitoses/HPF) |
