790 Identification of Hypermethylated Tumor-specific Deoxyribonucleic Acid in Plasma of Patients with Glioma

Abstract

INTRODUCTION: Although patients without malignancy have <100 ng/ml free deoxyribonucleic acid (DNA) in plasma, patients with malignancy demonstrate substantial quantities of tumor-specific DNA in their plasma. Measurements of this DNA are being studied to develop plasma markers to correlate with tumor burden. This approach has not been explored in gliomas. METHODS: Venous blood (30 ml) was collected before craniotomy from 10 patients with presumed glioma. After surgery, DNA was extracted and quantified from intracranial tumor and plasma samples. The methylation status of p16, p73, RAR&#61538, and MGMT gene promoters was assayed with methylation-specific polymerase chain reaction (MSP). The presence of tumor-specific DNA in the plasma was defined as identification of the same methylated promoter (MP) in both plasma and tumor. RESULTS: Pathological diagnoses were glioblastoma (n = 6), anaplastic astrocytoma (n = 2), anaplastic oligoastrocytoma (n = 1), and oligodendroglioma (n = 1). Total DNA concentration in plasma was grossly elevated (mean, 6503 ng/ml; standard error of the mean, 1400 ng/ml). Tumor specimens revealed methylation of at least one promoter in 9 of 10 patients (90%). Of the 9 patients with MP, 6 (67%) had methylation of at least one of the same promoters in the plasma DNA. Five of these had one MP identified in the plasma, and 1 had two MPs. Overall, glioma-specific methylated DNA was present in plasma of 6 of 10 patients (60%). Tumors with no plasma MP were two glioblastoma, one anaplastic astrocytoma, and one oligodendroglioma. No positive markers were found in the plasma that were not also found in the intracranial tumor. CONCLUSION: Gliomas shed large amounts of DNA into the blood. Using MSP, we found that tumor-specific DNA is present in plasma of glioma patients. This specific as promoter methylation is not found in normal tissue. Isolation of tumor-specific plasma DNA in these patients represents the first step to developing a quantitative glioma plasma biomarker that could be used to monitor tumor status.