Quantitative analysis of 06-methylguanine-DNA methyltransferase (MGMT) promoter methylation in patients with low-grade gliomas

Abstract

2069 Background: Loss of heterozygosity (LOH) on the chromosomes 1p and 19q is associated with sensitivity to alkylating agents like temozolomide (TMZ) in patients with low-grade gliomas; whether methylation of the MGMT-promoter, a predictive factor in glioblastoma patients, also correlates with tumor response to TMZ in low-grade gliomas is unclear. Methods: We performed a retrospective analysis of patients with histologically verified low-grade gliomas (WHO Grade II) who were treated with TMZ for tumor progression at our hospital between November 1999 and November 2007. Objective tumor response was assessed by MRI at 6-month intervals. LOH of microsatellite markers on chromosomes 1p and 19q was determined by polymerase chain reaction (PCR) amplification of the matched pairs of blood and tumor DNA. A methylation-specific, primer extension based PCR method was developed to quanitatively assess the MGMT methylation status in the tumour tissue. Results: Twenty-two patients with a median age of 53 years (range 27–72) were included in the study; 59% were male. Seven patients had prior surgical resection of the tumor. Histological classification revealed 10 oligodendrogliomas, 7 oligoastrocytomas, and 5 astrocytomas. All patients were treated with TMZ 200mg/m2 day1–5 in a 4 wk cycle. Grade 3–4 hematological toxicity occurred in 32% of the patients (9% leucopenia, 23% thrombocytopenia). The progression free survival was 32 months. Combined LOH 1p and 19q was found in 14 pts; 1 patient had LOH 1p alone and 1 patient LOH 19q alone. The LOH status could not be determined in two patients and was normal in the remaining four. MGMT promoter methylation was detectable in 20 pts by conventional PCR and quantitative analysis revealed a methylation status between 12%-100%. The volumetric response to chemotherapy analyzed after 6 months by MRI correlated with the level of MGMT promoter methylation (p = 0.012). Conclusions: Quantitative methylation-specific PCR of the MGMT promoter correlates with radiological response to chemotherapy with temozolomide in WHO grade II gliomas. No significant financial relationships to disclose.