SURG-41. PROGNOSTIC IMPACT OF EXTENDED RESECTIONS IN IDH MUTANT LOWER-GRADE DIFFUSE GLIOMA: RESULTS FROM A VOLUMETRIC ANALYSIS

Abstract

Abstract In IDH mutant (IDHmut) glioma, the prognostic impact of extended resections is still under debate. A potential outcome benefit may be influenced by the tumor’s molecular phenotype. Also, many studies lack objective quantitative assessment of residual tumor volume (RTV). Here, we analyzed the prognostic benefit of surgery in a molecularly defined cohort of patients harboring an astrocytoma or oligodendroglioma, IDHmut, WHO grade 2 and 3, for whom volumetric analysis of RTV was possible. Patient-, tumor- and treatment-related factors including pre- and post-operative MR FLAIR tumor volumes were correlated with progression-free (PFS) and overall (OS) survival. Confounders of resectability were analyzed by multiple linear regression. 206 patients treated at our institution over one decade were identified retrospectively. Mean age was 40.37 years. 105 patients suffered from IDHmut astrocytoma and 101 patients from oligodendroglioma. Resection (n = 185 patients; 89.8%) as opposed to biopsy was associated with prolonged PFS and OS in astrocytoma (p = 0.007; p = 0.038) and WHO grade 2 tumors (p = 0.012; p < 0.0001). In patients undergoing resection, median pre- and post-operative tumor volumes did not differ between tumor subtypes but were significantly larger in WHO grade 3 than 2 tumors (pre-operative: 71.3 vs. 28.8 cm3; RTV: 7.78 vs. 1.98 cm3). Median RTV of the complete cohort was 4.6 cm3. There was a stepwise improvement of outcome with decreasing RTV (PFS: p = 0.0003; OS: p = 0.0004; data given for quartiles), with the strongest effect observed for patients with no RTV (median PFS: undefined vs. 58 months; p = 0.007). In multivariable analysis, RTV independently predicted OS (p = 0.001; HR 1.012) but not PFS. Resectability was only influenced by pre-operative FLAIR tumor volume (p < 0.0001). In summary, a continuous association of RTV and outcome was observed, even at the highest levels of resection. This finding was more pronounced in astrocytoma. Thus, a maximal resection should be strived for whenever safely achievable.