Abstract C48: Detection of GNAQ/GNA11 mutations in circulating cell-free DNA as a biomarker of uveal melanoma.

Abstract

Abstract Background: Circulating tumor-derived DNA (ctDNA) can be detected in the plasma of cancer patients. Recently, ctDNA was proposed as a biomarker to follow tumor burden and monitor treatment efficacy (1). However, ctDNA represents a tiny fraction of the normal cell-free circulating DNA, and its assessment is challenging due to specificity, sensitivity and quantitative issues. Patients and methods: We developed a real-time PCR based on the pyrophosphorolysis-activated polymerization (bi-PAP) for the quantification of ctDNA in plasma of patients with uveal melanoma (UM). Bi-PAP can detect known point mutations independently of large excess of normal DNA (2). Our assay targets the activating mutation of codon 626 of GNAQ or GNA11 which are present in most UM (3, 4). Results: Bi-PAP primer pairs specific for GNAQ 626A>T, GNAQ 626A>C and GNA11 626A>T have been chosen. Their sensitivity and specificity were assessed on serial dilutions of tumor DNA in normal DNA. Each assay could detect a single mutated molecule per reaction, while 104 copies of normal DNA were not detected. In plasma of mice bearing UM xenografts, ctDNA were proportional to the amount of circulating human DNA and to the size of the xenograft. Furthermore, in a retrospective analysis of 19 UM patient sera, 8 were found positive. Conclusion: Bi-PAP represents a promising tool for the quantification of ctDNA in the blood of UM patients. A prospective study is on going to confirm the clinical value of ctDNA level in metastatic UM patients. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr C48.