Atypical Histopathological Features and the Risk of Treatment Failure in Nonmalignant Meningiomas: A Multi-Institutional Analysis

Biology and Treatment of Meningiomas: A Reappraisal

Meningiomas are largely indolent tumors with a benign clinical course, but a minority exhibit aggressive behavior characterized by rapid growth, neurologic deficits, and increased mortality. Identifying high-risk patients requiring intervention is challenging, but recent insights into meningioma biology provide a useful guide for decision making. Standard of care for recurrent or biologically aggressive tumors consists of surgery and radiation therapy. Systemic therapies targeting vascular endothelial growth factor signaling and somatostatin analogues are potential options for those with refractory disease but display only modest activity. New paradigms in meningioma clinical trial design provide hope for improved options in the future.

Treatment and follow-up results of WHO grade II meningiomas

Meningiomas are the most common primary intracranial tumors. They have three pathologic grades. Surgical resection aiming Simpson I resection is the standard treatment for meningiomas. Radiotherapy and Gamma Knife radiosurgery are the main adjuvant and salvage treatments. Chemotherapy has limited use. Grade II, and III meningiomas have a higher recurrence rate, and adjuvant radiotherapy is usually the standard treatment for grade III meningiomas but there is not a consensus regarding grade II meningiomas. In this paper, we analyzed our meningioma series of 1401 patients and presented the treatment and follow-up results of 170 grade II meningioma cases. The median follow-up of grade II meningiomas was 61 (range = 1-231) months. The mean age of patients was 52.5 ± 15.0 years, 102 of them were female and 68 were male (female/male ratio = 1.5). The median progression-free survival (PFS) of them was 109 months, and the cumulative overall survival (OS) rate was 85% at 10 years. Meningiomas with gross total resection, non-skull base meningiomas, and primary grade II meningiomas had longer PFS with statistical significance, while non-skull base meningiomas, younger group of patients, and primary grade II meningiomas had longer OS with a statistical significance.

Prognostic significance of brain invasion in meningiomas: systematic review and meta-analysis

The WHO 2016 classification introduced brain invasion as a standalone criterion for grade II meningioma (GIIM). We systematically reviewed studies published after 2000 and performed a PRISMA-compliant meta-analysis of the hazard ratios (HRs) for progression-free survival (PFS) between brain-invasive and noninvasive meningiomas. In five studies that included both benign and higher-grade meningiomas, brain invasion was a significant risk factor for recurrence (HR = 2.45, p = 0.0004). However, in 3 studies comparing "brain-invasive meningioma with otherwise benign histology (BIOB)" with grade I meningioma, brain invasion was not a significant predictor of PFS (HR = 1.49, p = 0.23). Among GIIM per the WHO 2000 criteria, brain invasion was a significant predictor of shorter PFS than noninvasive GIIM (HR = 3.40, p = 0.001) but not per the WHO 2016 criteria (HR 1.13, p = 0.54), as the latter includes BIOB. Meta-regression analysis of seven studies of grade II meningioma showed that more frequent BIOB was associated with lower HRs (p < 0.0001). Hence, there is no rationale for brain invasion as a standalone criterion for grade II meningioma, although almost all studies were retrospective and exhibited highly heterogeneous HRs due to differences in brain-tumor interface data availability.

Clear cell histology portends a worse prognosis than other WHO grade II histologies

PURPOSE

Clear cell meningioma (CCM) is a rare WHO grade II meningioma variant, characterized by aggressive features and a high tumor recurrence rate. In this study, we compared overall and progression-free survivals between CCMs and other WHO grade II meningiomas.

METHODS

A retrospective institutional database review was performed to identify all patients who underwent surgical resection of a WHO grade II meningioma between 1997 and 2019. Overall survival and progression-free survival were compared between patients with clear cell meningiomas and patients with other WHO grade II meningiomas. Multivariable Cox proportional-hazards analysis was used to identify independent predictors of tumor recurrence and survival.

RESULTS

We included a total of 214 patients in this study (43 CCMs, 171 other WHO grade II meningiomas). Patients with CCMs had significantly shorter progression-free (p = 0.001) and overall (p = 0.026) survivals than patients with other grade II meningiomas. In multivariable analysis, clear cell histology was a significant and powerful independent predictor of tumor recurrence (HR 1.93; 95% CI 1.14-3.26) when controlling for tumor location, extent of resection, and adjuvant radiation. In multivariable analysis, clear cell histology correlated with increased mortality (HR 1.96, 95% CI 0.97-3.94), though this was not statistically significant.

CONCLUSION

This is the first study to compare overall and progression-free survivals between CCMs and other WHO grade II meningiomas. Clear cell histology predicts a higher risk of tumor recurrence and mortality than other grade II histologies. Future studies may help to understand the impact of these findings and the treatment implications.