Microsatellite alterations plasma DNA of primary breast cancer patients

The aim of this study was to analyze plasma DNA from primary and metastatic breast cancer cases for tumor-specific alterations and to compare these findings with immunocytochemistry and estimation of cytokeratin 19 (CK19) mRNA for detection of micrometastases. DNA was extracted from plasma, lymphocytes, and microdissected tumor tissue sections obtained from 71 patients with breast cancer and 9 controls. DNA samples were analyzed for loss of heterozygosity (LOH) and/or microsatellite instability (MI) by PCR with two polymorphic markers (DM-1 and D16S400). Reverse transcription-quantitative PCR (QPCR) and immunocytochemistry were used for detection of CK19 mRNA and protein. Breast cancer plasma DNA displayed frequent LOH (31.3%) and MI (11.6%) supported by the same alteration in microdissected tumor DNA. Most notably, 10 of the 39 patients with primary breast cancer showed LOH (n = 6) or MI (n = 4). We compared plasma tumor DNA, plasma and bone marrow QPCR, and blood and bone marrow immunocytochemistry in 32 of the patients with primary cancer. Of these, only one patient had immunocytochemically detectable carcinoma cells in the blood, and three showed abnormally high levels of plasma CK19 mRNA. All four of these patients had plasma DNA alterations. We then compared bone marrow findings: of the 10 primary breast cancers that showed LOH or MI, 6 had elevated CK19 mRNA and 5 had immunocytochemically positive cells. Tumor DNA is readily detectable in plasma of primary and metastatic breast cancer patients, and plasma DNA alterations (LOH and MI) reflect those seen in the tumor. The application of microsatellite analyses to plasma DNA may be useful in assessing tumor burden in breast cancer patients, particularly when combined with QPCR, and is preferable for patients with breast cancer, for whom sequential bone marrow aspiration is undesirable.