The combination of mitotic and Ki-67 indices as a useful method for predicting short-term recurrence of meningiomas.

BACKGROUND

The most relevant factor in the progression-free survival (PFS) of patients with meningiomas is the malignant grade. However, using only the current World Health Organization (WHO) definition that does not consider precise quantitative indicators, an unequivocal diagnosis of the malignant grade is difficult. In our retrospective study of the PFS of meningioma patients, we focused on mitoses and the Ki-67 staining index of tumor specimens obtained at the initial surgery.

METHODS AND RESULTS

A total of 349 patients with intracranial meningioma, operated between 1978 and 2000, were followed for a mean of 7 years. According to the mitotic index (MI), we classified them into 3 groups. In Group A (n = 326), slide-mounted tumor samples exhibited no mitoses; in Group B (n = 15) there were fewer than 4 mitoses, and in Group C (n = 8) 4 or more mitoses were seen per 10 high-power fields (HPF). The estimated 5-year PFS rates in Groups A, B, and C were 93%, 10%, and 13% respectively. The mean PFS for Group A was 148 months; in Groups B and C the median PFS was 43 and 16 months, respectively. A Ki-67 staining index (SI) of less than 1% corresponded with no mitosis, while an SI exceeding 5% was indicative of the presence of mitoses.

CONCLUSION

In meningioma patients, no mitoses and/or a Ki-67 SI <1% signals a favorable outcome. An SI >5% or the presence of mitoses, even fewer than 4 in 10 HPF, is suggestive of a short PFS irrespective of other pathologic features. We suggest that in combination, assay of the Ki-67 SI and the MI represents a reliable, quantitative tool for predicting PFS in meningioma patients.