What is the risk of a meningioma becoming malignant?

From the Guidelines

Meningiomas have a low risk of becoming malignant, with only about 1-3% of all meningiomas classified as malignant (WHO grade III) 1. The vast majority of meningiomas (about 80-90%) are benign (WHO grade I), while approximately 5-15% are atypical (WHO grade II) with increased risk of recurrence but not necessarily malignant transformation. Certain factors may increase the risk of a more aggressive meningioma, including prior radiation exposure, certain genetic conditions like neurofibromatosis type 2, and specific histological features identified on pathology 1. Meningiomas with higher mitotic activity, brain invasion, or certain cellular patterns raise concern for atypical or malignant behavior. Regular monitoring with MRI scans is important for patients with known meningiomas to detect any changes in size or characteristics that might suggest malignant transformation. While most meningiomas grow slowly and remain benign throughout a patient's lifetime, those that do become malignant typically have a more aggressive clinical course requiring more intensive treatment approaches such as surgery, radiation therapy, and in some cases, systemic therapy. Some key points to consider in the management of meningiomas include:

• The role of radiation therapy, which may be used for WHO grade 1 and 2 meningiomas with doses of 45-54 Gy, and for WHO grade 3 meningiomas with doses of 54-60 Gy 1
• The use of stereotactic radiosurgery for small WHO grade 1 meningiomas with doses of 12-15 Gy in a single fraction 1
• The importance of multidisciplinary input for treatment planning, particularly for patients with complex or high-grade tumors 1

From the Research

Risk of Meningioma Becoming Malignant

• The risk of a meningioma becoming malignant is estimated to be 2.98/1000 patient-year 2.
• Malignant meningiomas, also known as WHO Grade III meningiomas, account for 1-3% of all intracranial meningiomas and have a poor prognosis with an overall survival of 2-3 years 3, 4.
• The median time to malignant progression is 4.3 years, but the cumulative rate of progression approaches a plateau after 10 years 2.
• Non-skull base location is a significant risk factor for progression to a higher grade 2.
• Radiosurgery does not appear to increase the incidence rate of malignant progression, but the risk may increase in patients with tumor-prone syndromes, such as neurofibromatosis type 2 2.

Factors Influencing Malignant Transformation

• Tumor location, with non-skull base location being a risk factor for progression 2.
• Presence of tumor-prone syndromes, such as neurofibromatosis type 2, which may increase the risk of malignant transformation after radiotherapy 2.
• Histologic grade, with higher grade meningiomas being more likely to become malignant 5, 3.

Treatment and Management

• Surgery is the main treatment for malignant meningiomas, while radiotherapy is thought to slow tumor growth 3.
• Chemotherapeutic agents, hormonal therapies, small molecule, and anti-angiogenic agents have been tried, but there is no robust evidence of efficacy 3.
• Stereotactic radiosurgery is a safe and effective treatment for meningioma, but its use in pediatric patients and those with tumor-prone syndromes is uncertain 6, 2.