Molecular pathogenesis of meningiomas.

Meningiomas are common central nervous system tumors that originate from the meningeal coverings of the brain and the spinal cord. Most meningiomas are slowly growing benign tumors that histologically correspond to World Health Organization (WHO) grade I. However, certain rare histological variants (clear cell, chordoid, papillary, and rhabdoid), as well as atypical (WHO grade II) and anaplastic (WHO grade III) meningiomas show a more aggressive biological behavior and are clinically associated with a high risk of local recurrence and a less favorable prognosis. This review summarizes the most important features of meningioma pathology and provides an up-to-date overview about the molecular mechanisms involved in meningioma initiation and progression. Current data indicate that meningioma initiation is closely linked to the inactivation of one or more members of the highly conserved protein 4.1 superfamily, including the neurofibromatosis type 2 gene product merlin/schwannomin, protein 4.IB (DAL-1) and protein 4.1R. The genetic alterations in atypical meningiomas are complex and involve losses on 1p, 6q, 10, 14q and 18q, as well as gains on multiple chromosomes. The relevant genes are still unknown. Anaplastic meningiomas show even more complex genetic alterations, including frequent alteration of the CDKN2A, p14ARF, and CDKN2B tumor suppressor genes at 9p21, as well as gene amplification on 17q23. A better understanding of the molecular mechanisms involved in meningioma pathogenesis may not only lead to the identification of novel diagnostic and prognostic marker but will also facilitate the development of new pathogenesis-based therapeutic strategies.