OLIGOASTROCYTOMAS - A CLINICOPATHOLOGICAL STUDY OF 52 CASES

Oligoastrocytomas form a poorly defined subgroup of glial tumors, and few clinical series have been reported. We performed a retrospective s tudy to elucidate the histopathological features of these tumors and t o relate the clinical signs and symptoms and proliferative potential t o survival. Oligoastrocytomas were defined as glial tumors with at lea st 10% neoplastic astrocytes and 10% neoplastic oligodendrocytes; tumo rs were graded with the St. Anne-Mayo criteria for astrocytomas and ol igodendrogliomas. Proliferative potential was estimated with antibodie s against proliferating cell nuclear antigen (PCNA). Median survival o f 52 patients (median age, 42 years) was 75 weeks (range 2-703 weeks). Actuarial 1-, 2-, 3-, and 5-year survival rates were 67%, 43%, 40%, a nd 29%, respectively. For 15 patients with grade 3 and 33 with grade 4 lesions (St. Anne-Mayo astrocytoma classification), median survival w as 217 and 55 weeks, respectively. For 19 patients with grade 2 and 33 with grade 3 lesions (St. Anne-Mayo oligodendroglioma classification) , median survival was 305 and 55 weeks, respectively. Interobserver ag reement between three experienced neuropathologists on identification of astrocytes, oligodendrocytes, and unclassifiable cells was low, ind icating considerable subjectivity in the histopathological diagnosis. Median PCNA labeling indices correlated with tumor grade, but individu al values varied so widely within grades that they had no predictive v alue for survival. In a multivariate analysis, symptoms of increased i ntracranial pressure and microvascular proliferation were independentl y associated with poor prognosis. The biological behavior of subgroups appeared to be distinctly less aggressive than that of 'pure' astrocy tomas of similar grade. Better histopathological definition of oligoas trocytomas and improved assessment of percentages of constituent cell types may allow more accurate prognosis.