O(6)-methylguanine DNA-methyltransferase (MGMT) in glioblastoma: Analysis on first and following surgeries.

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2097 Background: Glioblastoma (GBM) is the most common malignant primary brain tumor in adults. Outcome has recently improved with the introduction of post-operative concomitant chemoradiotherapy (CRT) followed by 6 cycles of temozolomide (TMZ). MGMT expression has already been encoded as an independent prognostic factor and predictive for TMZ sensitivity, but few data are available on the modifications of MGMT status after CRT. Methods: From January 2005 to November 2010 at Modena University Hospital and Nuovo Ospedale Civile S. Agostino-Estense, 15 consecutive patients (pts) with GBM and treated with at least 2 subsequent surgeries were included in this retrospective study. Aim of the present analysis is to evaluate if methylation status may change between first and following determinations. Results: Fifteen pts (M/F=10/5; median age: 48, range: 40-67 years) underwent a first surgery for GBM. MGMT status was: methylated in 5 (33%); unmethylated in 10 pts (77%). Two unmethylated pts presented an early relapse and underwent a second surgery after 41 and 46 days, respectively. MGMT analysis confirmed the absence of methylation. One pt with multifocal GBM was treated after the first surgery on right frontal lobe with TMZ, operated on left frontal lobe, submitted to CRT, then re-operated for a relapse in the first site of surgery (right frontal lobe). In this case MGMT status evaluated in the site of relapse (right frontal lobe) changed from unmethylated to methylated. MGMT on the lesion of left frontal lobe was unmethylated. The remaining 12 pts underwent post-operative concomitant CRT followed by monthly TMZ (median number of cycles: 8.5; range: 2-24). MGMT status on second surgery was: 5 methylated (42%) and 7 unmethylated (58%), with a 100% concordance. Two pts received a third surgery: in one case MGMT status changed from unmethylated to methylated. Overall median survival was 15.8 months. The two patients with “MGMT switch” have a median survival of 35.8 months. Conclusions: in 2 on 13 cases (15%) after CRT, MGMT status changed from unmethylated to methylated and these pts have a median overall survival similar to methylated pts. This observation may be confirmed on larger series.