P09.28 MGMT promoter methylation status in glioblastoma (GBM) patients: a quantitative pyrosequencing approach and its prognostic role

Background: MGMT gene promoter methylation status is acknowledged as a prognostic factor and predictive marker for temozolomide (TMZ) treatment. Although MGMT status determined by pyrosequencing was showed to correlate with progression free survival (PFS) and overall survival (OS), it is still unclear a cut-off value that discriminates between methylated and unmethylated patient (pts) and its correlation with the patient clinical outcome. Matherials and Methods: We analyzed the tissue samples from 128 PTS diagnosed with GBM from November 2009 to December 2015. All PTS underwent treatment with RT + TMZ and had an ECOG-PS 0-2. Methylation percentage for each sample was obtained by calculating the average methylation of all 10CpG sites (75-84) of MGMT promoter by pyrosequencing analysis. PTS with 0-6% of methylation were classified as unmethylated (UM), PTS with 7-24% as low methylated (LM) and PTS with ≥ 25% as high methylated (HM). 25% was the median value of methylation of our PTS having >6% of methylation. Results: Median age was 60 yrs (range 25-84), 60.9% were male, 74.2% had an ECOG PS 0-1, 50.8% underwent radical surgery, 85 PTS were dead at the time of analysis. 75 PTS were UM, 26 PTS were LM and 27 PTS were HM. On univariate analysis HM, LM and UM showed a PFS of 15.8, 10 and 9.1 ms, respectively (p=0.1). OS was 38.7, 21 and 18.8ms (p= 0.06). On multivariate analysis UM and LM PTS had a statistically lower PFS vs HM PTS (HR=2.57; p=0.001; HR= 2.5; p=0.007, respectively) and statistically lower OS (HR=3.47; p