Neuropathological and molecular aspects of low-grade and high-grade gliomas.

Gliomas are the most frequent primary brain tumors. They are derived from glial cells of astrocytic, oligodendroglial and ependymal origin. According to the WHO classification of brain tumors gliomas are divided in low-grade (grades I and II) and high-grade (grades III and IV) tumors. Low-grade tumors are well-differentiated, slow-growing lesions. Grade I tumors are well-circumscribed and often surgically curable, whereas grade II tumors are diffuse, infiltrating lesions with a marked potential over time for progression towards a high-grade malignant tumor. The optimal management of low-grade gliomas is still debated. Important prognostic factors such as histology, grade and location of the tumor, age and functional status of the patient, must be taken into consideration to select the most appropriate treatment. Major advances in the molecular genetic assessment of brain tumors and of gliomas in particular have lead to the identification of several molecular markers playing a crucial role in the development of gliomas and in their malignant transformation. Some of those markers were found very useful to assist in the histological diagnosis and to predict survival and response to therapy. A combined deletion of chromosomes arms 1p and 19q can be found in more than 50% of Grade II and III oligodendrogliomas and has been associated with chemosensitivity and a better prognosis. Once limited to the field of research, molecular biology has now entered the daily neuropathological practice and will undoubtedly play an increasing role in future classification and treatment of brain tumors.