Malignant meningioma: a clinicopathologic study of 23 patients including MIB1 and p53 immunohistochemistry.

Malignant meningiomas are rarely encountered neoplasms. Few studies have examined MIB1 (marker of cell proliferation) or p53 (tumor suppressor gene) immunoreactivity in these tumors. This study retrospectively examines 23 malignant meningiomas (defined by the presence of either unequivocal brain invasion or metastasis) including MIB1 and p53 immunohistochemistry. The patients included 13 women and 10 men who ranged in age from 22 to 82 years (mean 63 years). Initial clinical presentation included weakness or numbness in 10 patients, visual signs or symptoms in 7 patients, and headaches in 6 patients. Histologically, nuclear pleomorphism was present in 23 of 23 tumors, disorganized architecture in 22 of 22, necrosis in 20 of 23, prominent nucleoli in 17 of 23, and hypervascularity in 4 of 23. One to 18 mitotic figures per 10 high power fields (HPF) (mean 6.1) were observed. Metastases were present in six patients (bone: 3 patients; lung: 2 patients; skin: 2 patients; kidney: 1 patient; and liver: 1 patient). MIB1 indices (positive tumor cells per 1,000 tumor cells evaluated x 100) in 20 tumors ranged from 1.3 to 24.2 (mean 11.7). p53 nuclear staining was observed in only 2 of 20 tumors. Follow-up information was available in 21 patients: 6 died of tumor (mean 27 months); 9 are alive with residual tumor (mean 35 months); 5 are alive with no evidence of tumor (mean 12 months); and 1 died 13 days postoperatively. There was no obvious correlation of the MIB1 index and tumor behavior. The majority of malignant meningiomas are characterized by nuclear pleomorphism, architectural disorganization, necrosis, prominent nucleoli, and increased mitoses. MIB1 labeling in most malignant meningiomas was high, consistent with the generally rapid growth of these tumors. Only a rare malignant meningioma demonstrated p53 alteration by immunostaining.