Oligodendrogliomas: Reproducibility and prognostic value of histologic diagnosis and grading

Prognostic value of histological grading of oligodendroglial tumors is cont roversial and interobserver reproducibility in grading of these tumors is u nknown. Seven neuropathologists and 6 surgical pathologists experienced in brain tumor diagnosis assessed 124 oligodendroglial tumors operated at the Mayo Clinic (1960-1990). Among histologic parameters upon which current oli godendroglioma grading systems are based, only high cellularity, presence o f mitoses, microcalcifications, endothelial hypertrophy, endothelial prolif eration, and necrosis appeared to be reproducible. Reproducible histologic features, based on consensus ratings among neuropathologists (defined as >6 0%), were evaluated for the association with cause-specific survival by fit ting Cox regression models. By univariate analysis, a significant associati on with survival was found for age, high cellularity, presence of mitoses, endothelial hypertrophy and proliferation and necrosis. On multivariable an alysis with a stepwise variable selection method, only age and presence of endothelial proliferation were found to be independently associated with su rvival with a discriminatory index of the model of 0.68. Mitotic index was significantly associated with survival based on the grading from each separ ate neuropathologist, but it was not based on consensus, most likely becaus e this was classified as indeterminate in 54% of cases. Alternatively, "mod els fit" considering the assessment of single neuropathologists, identified a model based on age and on mitotic index with similar discriminatory indi ces of 0.69-0.7. Our study found few factors independently associated with cause specific-survival among morphological parameters. These findings are consistent with the present WHO stratification of oligodendrogliomas into l ow- and high-grade variants.