Grading of gliomas: the road from eminence to evidence.

The development of concise grading schemes for diffuse gliomas with proven relevance to tumor behavior and susceptibility to therapy is important for clinical decision making. At present, there is unacceptably large interobserver discrepancy in the application of the current World Health Organization (WHO) criteria for accrual of patients in trials for patients with gliomas. Because of a lack of relevant studies, the WHO guidelines for grading are not yet as clear as would be desirable. The development of well-defined grading schemes consisting of features with low interobserver scoring variability and prognostic or predictive relevance is needed. Although interobserver concordance can be tested in retrospective studies, the prognostic or predictive qualities of histological parameters can only be tested in prospective studies. Only evidence-based histopathology will retain its critical role in the diagnosis and treatment of diffuse gliomas.