Methylated tumor-specific DNA as a plasma biomarker in patients with glioma

Abstract

1527 Background: While patients without malignancy have <100μg/ml free DNA in plasma (Chang, J NC I 2002), 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: This study assesses the presence of plasma tumor-specific DNA in gliomas using methylation specific polymerase chain reaction (MSP). With IRB approval, 30 ml venous blood was collected prior to craniotomy from 10 patients with presumed high grade glioma. After surgery, DNA was extracted and quantified from the tumor and plasma samples. The methylation status of p16, p73, RARβ, and MGMT gene promoters was assayed with 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: Histology was: glioblastoma (N=6), anaplastic astrocytoma (2), anaplastic oligoastrocytoma (1), grade II oligodendroglioma (1). Total DNA concentration in plasma was grossly elevated (mean 6503 μg/ml, SEM 1400μg/ml). Surgical specimens revealed methylation of at least one promoter in 9/10 (90%) of patients. Six pts had 1 MP, 2 had 2 MP, and 1 had 3 MP. The one patient with no identified MP had glioblastoma. 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 1 MP identified in the plasma and 1 had 2 MP. Overall, glioma-specific methylated DNA was present in plasma of 6/10 (60%) patients to date. Tumors with no plasma MP were 2 glioblastoma, 1 anaplastic astrocytoma and 1 oligodendroglioma. No positive markers were found in the plasma that were not also found in the intracranial tumor. Conclusions: Gliomas shed large amounts of DNA into the blood. Using MSP, we found that tumor-specific DNA can be identified in plasma of high grade glioma patients. This is likely to be quite 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. No significant financial relationships to disclose.