Impact of extent of resection on outcome from glioblastoma using the RANO resect group classification system: a retrospective, population-based cohort study

BACKGROUND: Extent of resection (EOR) is associated with survival in glioblastoma. A standardized classification for EOR was lacking until a system was recently proposed by the response assessment in neuro-oncology (RANO) resect group. We aimed to assess EOR in an unselected glioblastoma cohort and use this classification system to evaluate the impact on survival in a real-world setting. METHODS: We retrospectively identified all patients with histologically confirmed glioblastoma in Western Norway between 1.1.2007 and 31.12.2014. Volumetric analyses were performed using a semi-automated method. EOR was categorized according to the recent classification system. Kaplan–Meier method and Cox proportional hazard ratios were applied for survival analyses. RESULTS: Among 235 included patients, biopsy (EOR class 4) was performed in 50 patients (21.3%), submaximal contrast enhancement (CE) resection (EOR class 3) in 66 patients (28.1%), and maximal CE resection (EOR class 2) in 119 patients (50.6%). Median survival was 6.2 months, 9.2 months, and 14.9 months, respectively. Within EOR class 2, 80 patients underwent complete CE resection (EOR class 2A) and had a median survival of 20.0 months, while 39 patients had a near-total CE resection, with ≤1 cm(3) CE residual volume (EOR class 2B), and a median survival of 11.1 months, P < 0.001. The 2-year survival rate in EOR class 2A was 40.0%, compared to 7.7% in EOR class 2B. CONCLUSIONS: RANO resect group classification for the extent of resection reflected outcome from glioblastoma in a real-world setting. There was significantly superior survival after complete CE resection compared to near-total resection.