P17.01.A THE ROLE OF DEXAMETHASONE DURING TREATMENT PHASES IN GLIOBLASTOMA: INSIGHTS FROM A RETROSPECTIVE OBSERVATIONAL STUDY

Abstract BACKGROUND Glioblastoma is the most aggressive primary brain tumour and is often associated with severe perifocal oedema. Corticosteroids such as dexamethasone (DEX) are used to counteract this oedema. However, the impact of DEX on overall survival (OS) and progression-free survival (PFS) at different stages of treatment has not been well studied. MATERIAL AND METHODS We conducted a single-centre retrospective study to analyse the impact of DEX on OS and PFS in GBM patients in the pre-operative, post-operative and adjuvant treatment phases. Data were collected from 106 patients treated between 2016 and 2020. Survival outcomes were analysed using Kaplan-Meier estimates and Cox proportional hazards models, with cut-off analyses to determine thresholds for DEX dosing in each treatment phase. RESULTS Preoperatively, DEX had no effect on OS and PFS (HR: 0.998, p = 0.379 for OS; HR: 0.998, p = 0.373 for PFS). However DEX in the postoperative period had a positive effect on OS (HR: 0.995, p = 0.017) and PFS (HR: 0.995, p = 0.029). In the adjuvant setting, DEX appeared no negative effect on OS and PFS (HR: 1.001, p = 0.069 for OS; HR: 1.001, p = 0.258 for PFS). Group comparisons in the adjuvant setting showed that patients who did not receive DEX had a better OS (17.9 months vs. 6.4 months, p < 0.001) and PFS (9 months vs. 4.6 months, p = 0.007). The exploratory determination of cut-off values showed that a DEX dose of at least 60 mg preoperatively (OS: 4.9 months vs. 9.4 months, p = 0.007) and up to 140 mg postoperatively (OS: 6.3 months vs. 10.8 months, p = 0.039) and less than 40 mg during adjuvant therapy (OS: 5.8 months vs. 15.9 months, p = 0.0003; PFS: 4.6 months vs. 9 months, p = 0.007). CONCLUSION DEX administration has a different effect on OS and PFS depending on the treatment phase. Higher doses postoperatively are associated with better survival, while DEX during adjuvant treatment correlates with a worse outcome. Careful dosing of DEX is critical in the treatment of GBM. This highlights the need for cautious use of corticosteroids and further studies to determine optimal dosing strategies.