SURG-19. PROGNOSTIC VALIDATION OF A NEW CLASSIFICATION SYSTEM FOR EXTENT OF RESECTION IN GLIOBLASTOMA: A REPORT OF THE RANO RESECT GROUP

Abstract

Abstract BACKGROUND Terminology to describe extent of resection in glioblastoma is inconsistent across clinical trials. A surgical classification system was previously proposed based upon residual contrast-enhancing (CE) tumor. We aimed to (I) explore the prognostic utility of the classification system and (II) define how much removed non-CE tumor translates into a survival benefit. METHODS The international RANO resect group retrospectively searched the databases from seven neuro-oncological centers in the USA and Europe for patients with newly diagnosed glioblastoma per WHO 2021 classification. Clinical and volumetric information from pre- and post-operative MRI were collected. RESULTS We collected 1021 patients with newly diagnosed glioblastoma, including 1008 IDHwt patients. 744 IDHwt glioblastomas were treated with radiochemotherapy per EORTC 26981/22981 (TMZ/RT→TMZ) following surgery. Among such homogenously treated patients, lower absolute residual tumor volumes (in cm3) were favorably associated with outcome: patients with ‘maximal CE resection’ (class 2) had superior outcome compared to patients with ‘submaximal CE resection’ (class 3) or ‘biopsy’ (class 4) (median OS: 19 versus 15 versus 10 months; p=0.001). Extensive resection of non-CE tumor (≤ 5 cm3 residual non-CE tumor) provided an additional survival benefit in patients with complete CE resection, thus defining class 1 (‘supramaximal CE resection’) (median OS: 24 versus 19 months; p=0.008). The prognostic value of the resection classes was retained on multivariate analysis when adjusting for molecular and clinical markers including MGMT promotor status. Relative tumor reduction (in percentage) was not prognostic for outcome on multivariate analysis, and inter-rater agreement for CE and non-CE tumor on post-operative MRI was sufficient. CONCLUSION The proposed “RANO categories for extent of resection in glioblastoma” are highly prognostic and may serve for stratification of clinical trials. Removal of non-CE tumor beyond the CE tumor borders translates into additional survival benefit, providing a rationale to explicitly denominate such a ‘supramaximal CE resection’.