P14.86 Predictive value of MGMT promoter (pMGMT) methylation status on pseudoprogression (PsP) and survival analysis in Glioblastoma (GBM) patients: a retrospective single institutional analysis
Abstract BACKGROUND Glioblastoma is the most common and aggressive primary brain tumor. Conventional therapies, such as maximal extension of surgery followed by radiotherapy (RT) and chemotherapy with Temozolomide (TMZ) have not resulted in major improvements in terms of patients’ outcome, overall survival (OS) still remaining poor. In this context, radiological response assessment after radiotherapy remains challenging due to the potential effect of radionecrosis, often mimicking tumor progression. Differentiation between PsP and true progression is required to avoid further unnecessary surgeries, or the premature discontinuation of TMZ. It is known that pMGMT methylated patients respond better to chemotherapy than unmethylated counterpart, so, tumor cells necrosis can be enhanced in this setting. The aim of the study is to observe the correlation between pMGMT methylation status with the incidence of PsP in GBM patients at the first radiological evaluation after RT. MATERIALS AND METHODS Patients with histologically diagnosis of GBM from 2017 to 2021 and availability of pMGMT methylation status were enrolled. PsP was radiologically defined at first brain MRI after RT in case of increasing size of the enhancing component and of peritumoral oedema that remain stable or decrease after antioedema therapy, such as a clinical improvement was observed. RESULTS We analysed 55 GBM patients, 35 (64%) displayed pMGMT methylation whereas 20 (36%) resulted pMGMT unmethylated. PsP was evident in 29 patients (53%), all of them showed methylation of pMGMT. In our analysis, none of pMGMT unmethylated patients experienced PsP. Regarding survival outcome for pMGMT methylated patients, our analysis shows a mPFS of 8.7 (95% CI: 5–10) months versus 9.3 (95%CI: 4.6–12.3) months in methylated and unmethylated respectively (p=0.87). CONCLUSIONS Methylation status of pMGMT showed to be predictor of PsP in GBM patients. If validated, this information could be very useful to guide clinicians in differentiating PsP from true progression. To date, our survival analysis regarding PFS showed no statistical difference among methylated patients with respect to the presence or absence of PsP. Thus, PsP seems not to be a marker of responsiveness to common treatment. Further data are needed to validate our results.