Progress in long-term survival in adult patients with supratentorial low-grade gliomas: a population-based study of 993 patients in whom tumors were diagnosed between 1970 and 1993

Object. The goal of this study was to document and compare long-term survival during the periods 1970 through 1981 and 1982 through 1993 in all adult patients in Norway with histologically verified supratentorial low-grade gliomas (LGGs). Methods. Nine hundred ninety-three patients 15 to 69 years of age were found to have a primary supratentorial diffuse astrocytoma, oligodendroglioma, oligoastrocytoma, or pilocytic astrocytoma. Survival time was analyzed in all patients and, in a subset of 451 patients, the influence of new imaging methods on the time from symptom onset to imaging diagnosis was estimated. Overall median survival was 6.4 years (95% confidence interval [CI] 5.7-7.1 years). Survival times for patients in whom a diagnosis was made between 1970 and 1981 (397 patients) and between 1982 and 1993 (596 patients) were 4.1 years (95% CI 3.3-4.9 years) and 9.2 years (95% CI 7.9-10.6 years), respectively (p < 0.0001). Survival also improved in the later period within each histological subgroup. In patients in whom a biopsy was performed the median length of survival was 6.4 years (95% CI 3.1-9.7 years); in patients treated with subtotal tumor resection it was 6.8 years (95% CI 5.8-7.7 years); and in those treated with gross-total tumor resection it was 7.6 years (95% Cl 5.5-9.7 years), a nonsignificant difference (p = 0.59). A considerable age-dependent variation in overall survival was demonstrated. The availability of computerized tomography (CT) scanning and/or magnetic resonance (MR) imaging as a diagnostic tool reduced the median period of symptoms prior to diagnosis by 6 months. Conclusions. Long-term overall survival significantly improved, but age-related differences in prognosis persisted. The increased sensitivity of the diagnostic method due to the availability of CT scanning and/or MR imaging may partly, but not entirely, account for the observed magnitude of improvement in overall survival. Thus local tumor treatment improved during the study period.