PATH-12. CLINICAL AND NEUROPATHOLOGICAL MARKERS FOR DISTINGUISHING BETWEEN IDH-MUTANT ASTROCYTOMAS OF WHO GRADE 2 AND 3

Abstract BACKGROUND The neuropathological criteria of anaplasia to distinguish between IDH-mutant astrocytomas of WHO grade 2 and 3 are ill-defined by the WHO 2021 classification. Following the positive phase III trial results and the expected approval of Vorasidenib for grade 2 astrocytomas, identifying prognostic markers distinguishing grade 2 and 3 tumors remains crucial. METHODS We retrospectively searched our institutional database for patients meeting the diagnostic criteria for IDH-mutant astrocytomas per the WHO 2021 classification. Clinical, neuropathological, and molecular data were collected, and outcomes compared using log-rank analysis. Centralized slide review is ongoing to exclude inter-rater variability due to the study’s retrospective nature. RESULTS We identified 99 patients with IDH-mutant astrocytomas in which detailed neuropathological and clinical information were available for review, including 63 tumors (63.6%) which were assigned to WHO grade 2 and 36 tumors (36.4%) assigned to WHO grade 3. At a median follow-up of 7.5 years, median progression-free survival was 5.7 years for WHO grade 2 tumors and 4.4 years for WHO grade 3 tumors. Median overall survival for WHO grade 2 and WHO grade 3 tumors was not reached. On univariate analysis, higher WHO grade, an increased number of mitoses, elevated Ki67 indices and the presence of contrast-enhancement on pre-operative imaging were associated with less favourable outcome. However, only the presence of contrast-enhancement retained its prognostic significance when forwarded into a multivariate model (p = 0.034 for overall survival, p = 0.012 for progression-free survival). The findings on the association between contrast-enhancement and outcome were confirmed in treatment-based subgroups, including individuals treated with a watch-and-scan approach (n = 30), radiotherapy (n = 25), or chemotherapy (n = 33). CONCLUSION While our findings await confirmation in larger prospective cohorts, neuropathological criteria for anaplasia might need to be accompanied by clinical information including contrast enhancement to prognostically distinguish grade 2 from grade 3 tumors particularly in patients undergoing biopsy given the risk for undersampling.