Quantitation of circulating DNA in the serum of breast cancer patients by real-time PCR

The purpose of this study was to quantify the level of serum DNA in different groups of primary breast cancer patients and in healthy controls using real-time quantitative PCR in order to determine whether such measurements have diagnostic or prognostic value. A total of 96 serum samples of patients with primary breast cancer before surgery (with positive or negative lymph nodes and with high or low relapse-free survival) as well as 24 healthy controls were analysed. DNA concentrations in the serum of the patients differed significantly from the concentration of serum DNA in the controls (medians were 221 and 63 ng ml−1, respectively, P<0.001 M–W test). However, no statistically significant difference was observed between the patient groups (P=0.87, M–W test). The serum DNA levels were elevated independently of the size of primary tumour or lymph node metastases. The overall survival of patients with serum DNA concentrations >221 ng ml−1 was better than patients with serum DNA concentration ⩽221 ng ml−1 (Kaplan–Meier, P=0.028).