TMIC-14. RAPID EARLY PROGRESSION IN GLIOBLASTOMA: A COMPREHENSIVE REVIEW OF CLINICAL, IMAGING AND HISTOPATHOLOGICAL FEATURES

Abstract

Abstract BACKGROUND In glioblastoma patients, Rapid Early Progression (REP) refers to tumour growth between the time of surgery and postoperative chemoradiotherapy. Despite its high incidence relatively little is known about it. The aim of this study was to characterise REP using a combination of clinical, imaging and histopathology data. METHODS Ethical approval was obtained. Supratentorial IDH-wildtype glioblastomas undergoing gross-total resection (GTR) between 2015-2021 were included. REP was defined as a nodular increase in enhancement located within or around the surgical cavity, occurring within 6 weeks of surgery, that was not accounted for by initial areas of diffusion-restriction. REP cases were propensity-score matched to controls on baseline characteristics. Imaging was compared using mean apparent diffusion coefficient (ADC) and T1-postcontrast radiomics. Tissue analyses included DNA methylation subtyping and immunohistochemistry for markers of T-cells (CD3), microglia (P2RY12) and proliferation (PHH3). RESULTS REP occurred in 8/60 GTR cases (13%) and these patients were matched to 16 controls. REP cases had a worse preoperative performance status (median Eastern Cooperative Oncology Group [ECOG] 2 vs. 1), overall-survival (p=0.038) and progression-free survival (p = 0.029). REP was more common in patients over 65 years (27%) and significantly fewer REP patients received radical postoperative chemoradiotherapy (p=0.023). REP and control cases were well matched with respect to preoperative T1-postcontrast radiomics and mean ADC in enhancing (p=0.99) and non-enhancing regions (p=0.67). There was no relative excess of any one DNA methylation subtype in REP cases. The two groups had a similar proportion of T-cells (p=0.81), but REP cases had a trend towards a higher proportion of microglia (31% vs. 17%; p=0.22), and a lower proliferation rate (3% vs. 9%; p=0.19). CONCLUSION REP cases had a worse performance status from diagnosis and received less radical postoperative chemoradiotherapy protocols compared to controls, yielding a significantly shorter median OS/PFS. Differences in immune landscape and proliferation rate should be further investigated.