gms | German Medical Science

Objective: Malignant glioma of the posterior fossa is a rare localization and accounts for 1% of all glioma cases. Compared with malignant gliomas of the hemispheres, the prognosis of the infratentorial counterpart seems to be slightly better. Low expression rates of EGFR are supposed to be predictors for long-time survival. In general IDH 1/2 status and MGMT promotor methylation in gliomas were identified as prognostic factors. We wondered if these molecular signatures offer also a strong prognostic value in this special subgroup of malignant gliomas.

Method: We performed a single institutional review of tumor samples and retrospectively identified 14 patients diagnosed with malignant infratentorial gliomas between 1998 and 2013. The presence of IDH 1/2 mutation and MGMT promotor methylation status were analysed and correlated to individual localization within the posterior fossa, treatment regimes, age, median and overall survival rate. A historical series of supratentorial malignant gliomas served for comparative reasons as well as one in-house series.

Results: The arrangement concerning male and female patients was balanced (7:7). The average age on time of diagnosis was 51 years in male patients and 54 years in the female group. More than 70% of the infratentorial tumors showed no MGMT promotor hypermethylation. Over 80% of the tumors did not harbor IDH-1/2 mutations, suggesting that these tumors are of primary origin. Despite these facts both, the overall survival rate and the median overall survival were remarkable extended in patients with infratentorial gliomas compared to supratentorial localization after surgery and adjuvant therapy. Absence of brainstem invasion was also identified as a prognostic factor.

Conclusions: MGMT promotor methylation and absence of IDH1/2 mutations are associated with a shorter median overall survival of patients with supratentorial malignant gliomas. However, patients with high-grade gliomas located in the posterior fossa seem to offer a better prognosis, despite their molecular characteristics. In addition absence of brainstem invasion was also confirmed as a prognostic factor in our series.