Background: The aim of this study was to investigate survival times and 4 prognostic factors of oligodendrogliomas in the CT/MR-era, since most previous studies result from the pre-CT-era, where modern histopathological classification, diagnostic and therapeutic tools were not used. Thus, in the past mixed gliomas were included, and survival times and prognostic factors were not corrected for grades.
Method: We present a retrospective study of 19 pure low grade (LO) and 21 pure anaplastic (AO) oligodendrogliomas (according to WHO) treated in the CT/MR-era 1987 to 1999. Survival times and rates were calculated in each grade according to the Kaplan-Meier-method. Following factors were analyzed for influence on survival in each grade using uni- and multivariate analysis: KI (karnofski index) equal or greater than 80 at time of diagnosis, contrast medium enhancement and calcification in preoperative CT or MRI, radiation therapy.
Findings: In LO median survival time was 114 months and 5 and 10-year survival rates were 78.9 and 44.1%, respectively. For AO median survival time was 21 months and 5- and 10-year survival rates were 23.8% and 0.05%, respectively. This difference reached statistical difference (p=0.0002). In LO none of the factors were statistically associated with better survival. Patients with AO had a significantly better outcome, when presenting with a KI of 80 or higher (uni- and multivariate analysis), than had tumours without contrast medium uptake (univariate) and for those with radiation therapy (univariate and multivariate).
Interpretation: In the CT/MR-era we did not observe a longer survival time or rate for patients with pure oligodendrogliomas compared to historical data. Prognostic factors should be evaluated separately in each grade, since grading according to WHO is strongly associated with survival. Patients with AO had a statistically longer survival when presenting with higher KI, without contrast enhancement and after postoperative radiation therapy.