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OBJECTIVE Meningioma is the most common primary intracranial neoplasm. Only 1%–3% of meningiomas are malignant according to the 2016 WHO criteria (WHO grade III). High-grade meningiomas present specific gene expression signatures indicating aggressive growth or recurrence. However, changes in gene expression and in neuroinflammatory gene expression signatures in WHO grade III meningiomas and during progression from WHO grade I or II to grade III are unknown. METHODS The authors used a NanoString targeted gene expression panel with focus on 787 genes relevant in meningioma pathology and neuroinflammatory pathways to investigate patients with grade III meningiomas treated at Rigshospitalet from 2000 to 2020 (n = 51). A temporal dimension was added to the investigation by including samples from patients’ earlier grade I and II meningiomas and grade III recurrences (n = 139 meningiomas). The authors investigated changes in neuroinflammatory gene expression signatures in 1) grade I meningiomas that later transformed into grade III meningiomas, and 2) grade III meningiomas compared with nonrecurrent grade I meningiomas. RESULTS The authors’ data indicate that FOXM1, TOP2A, BIRC5, and MYBL2 were enriched and the HOTAIR regulatory pathway was enriched in grade III meningiomas compared with nonrecurrent grade I meningiomas. They discovered a separation of malignant and benign meningiomas based only on genes involved in microglia regulation with enrichment of P2RY12 in grade I compared with grade III meningiomas. Interestingly, FOXM1 was upregulated in premalignant grade I meningioma years before the grade III transformation. CONCLUSIONS The authors found gene expression changes in low-grade meningiomas that predated histological transformation to grade III meningiomas. Neuroinflammation genes distinguished grade III from grade I meningiomas., OBJECTIVE: Meningioma is the most common primary intracranial neoplasm. Only 1%-3% of meningiomas are malignant according to the 2016 WHO criteria (WHO grade III). High-grade meningiomas present specific gene expression signatures indicating aggressive growth or recurrence. However, changes in gene expression and in neuroinflammatory gene expression signatures in WHO grade III meningiomas and during progression from WHO grade I or II to grade III are unknown.METHODS: The authors used a NanoString targeted gene expression panel with focus on 787 genes relevant in meningioma pathology and neuroinflammatory pathways to investigate patients with grade III meningiomas treated at Rigshospitalet from 2000 to 2020 (n = 51). A temporal dimension was added to the investigation by including samples from patients' earlier grade I and II meningiomas and grade III recurrences (n = 139 meningiomas). The authors investigated changes in neuroinflammatory gene expression signatures in 1) grade I meningiomas that later transformed into grade III meningiomas, and 2) grade III meningiomas compared with nonrecurrent grade I meningiomas.RESULTS: The authors' data indicate that FOXM1, TOP2A, BIRC5, and MYBL2 were enriched and the HOTAIR regulatory pathway was enriched in grade III meningiomas compared with nonrecurrent grade I meningiomas. They discovered a separation of malignant and benign meningiomas based only on genes involved in microglia regulation with enrichment of P2RY12 in grade I compared with grade III meningiomas. Interestingly, FOXM1 was upregulated in premalignant grade I meningioma years before the grade III transformation.CONCLUSIONS: The authors found gene expression changes in low-grade meningiomas that predated histological transformation to grade III meningiomas. Neuroinflammation genes distinguished grade III from grade I meningiomas.

OBJECTIVE WHO grade III meningiomas, also known as malignant meningiomas (MMs), are rare, and the heterogenous clinical course in patients with MM is not well described. To characterize the clinical course of patients with MM, granular clinical data were gathered from 51 patients treated at the Department of Neurosurgery and Radiation Oncology, Rigshospitalet, in Copenhagen, Denmark, between 2000 and 2020. METHODS The authors investigated outcome and timing in terms of 1) tumor progression and grade transformation in patients previously diagnosed with WHO grade I or II meningiomas (patients with a secondary MM [sMM]); 2) performance status and complications following surgery; and 3) transition to noncurative treatment and ultimately death. Complications, time between recurrences, and outcome (modified Rankin Scale [mRS] score) for every surgery were analyzed, both malignant and premalignant. RESULTS Of the 51 patients, 24 (47%) had an sMM. The time to WHO grade III transformation in the sMM group varied widely (median 5.5 years, range 0.5-22 years), but after transformation to a WHO grade III tumor, patients with an sMM and those with a primary MM (pMM) did not differ significantly in overall survival and cumulative risk of progression. Median overall survival for all 51 patients was 4.2 years (95% CI 2.6-7.2 years). Time from the decision to shift from curative to noncurative treatment until death was 3.8 months and the 30-day mortality rate following surgery was 11.8%. From a cumulative number of 151 surgeries, 10 surgeries were followed by improvement on the mRS, mRS score was unchanged in 70, and it worsened in 71. The MM was the underlying cause of death in 30 of 31 patients who had died at the end of follow-up. CONCLUSIONS Together, these findings clearly show a significant morbidity and mortality from the disease itself and from the treatment. These findings warrant studies of prognostic factors for earlier support and adjuvant measures in MM and identify

The stem cell marker CD133 has been sporadically investigated in meningioma, but because of the rarity of malignant meningioma (WHO grade III), only 7 malignant meningioma specimens have been included in previous studies. We investigated CD133 expression using the AC133 antibody clone in a consecutive cohort of 38 malignant meningiomas. Our results showed few, small CD133-positive hot spots with a pattern dominated by membranous staining and capping of the proteins without any nuclear CD133 staining in 30 of the 38 tumors. We could not corroborate spatial co-expression of hot spots with the proliferative marker, Ki-67, and CD133 hot spots in adjacent slides, nor did we find differences between Ki-67 expression in CD133-negative and -positive tumor specimens (Fisher’s exact test: p = 0.69). CD13-positive niches represented only 0 – 1% of meningioma cells in most of the malignant meningioma, while CD133-positive cells were undetectable in 21% of the whole-section tumor samples. We found stem cell niches in 79% of malignant meningioma specimens in our cohort.