Analysis of serial plasma DNA samples in terms of lost of heterozygosity (LOH) and microsatellite instability (MI), used as tumor markers during follow up of women with primary breast cancers.

Abstract

3283

Purpose: The development of a blood test that can detect cancer or predict disease outcome is an ongoing challenge. One possibility is to use recent knowledge of cancer genetics to develop a simple test applicable to blood samples. The identification of DNA exhibiting tumor specific LOH in plasma from patients with lung and head and neck cancers respectively prompted a wider investigation of other cancer types. Several groups, including our own, identified specific microsatellite alterations, principally LOH, in plasma and/or serum from patients with breast cancer. Moreover, two of these studies suggested that tumor DNA in plasma at diagnosis may be a valuable predictor of disease free-survival The aim of this study was to investigate the utility of plasma DNA analysis for follow up of primary breast cancer patients. Patient and Methods: Blood samples were taken over a period of 2 years following diagnosis from 10 patients with primary breast cancer and over 6 months from 10 patients with metastatic breast cancer . DNA was extracted from lymphocytes, plasma and foci of tumor cells, isolated by laser capture microdissection, and analysed for tumour specific LOH at four loci (DM-1, D17S855, D13S260, D10S249) previously shown to exhibit frequent LOH in breast cancer cases. Double-stranded plasma DNA was also quantified using Pico green fluorescence measurement. Results: All 10 patients who had primary breast cancer had detectable DNA in all plasma samples collected, with variable concentrations but tending to increase with time after diagnosis. 2 had plasma DNA samples taken before breast cancer resection that showed tumor specific alterations (LOH identical to that seen in the tumour). Both of these patients relapsed within 1 year; one has since died and one has developed metastases. The 8 other primary patients remain disease-free 3 years after diagnosis, 5 now show LOH in plasma DNA, which has remained consistent in at least 2 of 3 subsequent plasma samples. The 10 patients with metastatic breast cancer have DNA with consistent tumour specific alterations detected in all plasma samples tested. Conclusions: This pilot study suggests that identifying plasma DNA with LOH at diagnosis in primary patients may be a useful prognostic indicator where there are no other clinical signs of metastatic disease and warrants further investigation in a larger series of patients.