RARE-23. INFRATENTORIAL GLIOBLASTOMA: INCIDENCE AND ASSOCIATED PROGNOSTIC FACTORS AMONGST OVER 1000 CONSECUTIVE GLIOBLASTOMAS

Abstract

Infratentorial glioblastoma is rare in adults. We analyzed glioblastomas resected at our institution 2004-2014 to determine any distinguishing characteristics of infratentorial glioblastomas. Glioblastomas cases involving cerebellar parenchyma were reviewed. 58 newly diagnosed glioblastomas with cerebellar involvement fell into 3 cohorts: (1) purely cerebellar glioblastomas (n=11=19.0%); (2) glioblastomas that began supratentorial and developed infratentorial tumor in continuity with supratentorial tumor (n=28=48.3%); (3) glioblastomas that began supratentorial and developed infratentorial tumor at a distant site from supratentorial tumor (n=19=32.7%). Mean ages at cerebellar glioblastoma diagnosis, gender distribution, and diameter of the cerebellar glioblastoma were 49.4,57.21,53.2 years(P=0.19), 55%,57%,53% Males (P=0.4), 3.5,2.6,1.5 cm (P=0.002) for cohorts 1,2,3 respectively. The most common preoperative symptoms were: ataxia (n=9) and headache (n=8). Surgical procedures were: biopsy (9%), STR (73%), and GTR (18%). 18% of patients developed hydrocephalus needing shunt placement a mean of 4.5 months after diagnosis. Median OS from GBM diagnosis for the 3 cohorts was 10.6,12.4,16.5 months, compared to 15.8 months for purely supratentorial GBMs(P= 0.04, 0.6, 0.4 respectively). We performed focal analyses of patients with supratentorial GBMs who developed cerebellar foci (cohorts 2/3). Median time from diagnosis of supratentorial GBM to developing infratentorial GBM was 4.5,10 months (P=0.4).16.8%,25.0% (P=0.02) patients received bevacizumab, and 28.6%,31.8% (P=0.04) received GTR in cohort 2,3. The most common sites of supratentorial tumor were temporal (45%), frontal (62%). Median OS from identification of infratentorial GBM was 6,7 months. Purely cerebellar glioblastomas at diagnosis conferred a better prognosis than supratentorial GBMs. Local or distant spread of supratentorial GBMs to the cerebellum did not worsen prognosis, with the latter occurring earlier in the disease course. Purely cerebellar glioblastomas should be treated aggressively given their good prognosis.