Background: The integrity of circulating cell-free DNA (cf-DNA) in serum or plasma appears to be of diagnostic and prognostic value in cancer. Here, we investigated the dynamics of serum DNA levels and the size distribution of cf-DNA during adjuvant chemotherapy of patients with breast cancer (n=73).
Methods: By evaluating sera taken at the beginning and the end of the adjuvant chemotherapy, variations of serum DNA levels and the size distribution were analyzed, based on quantification of shorter apoptotic and longer non-apoptotic fragments from abundant genomic ALU fragments amplified by quantitative real-time PCR.
Results: The mean DNA level did not change significantly during chemotherapy. However, individual cases revealed considerable variation in the amount of serum DNA. It increased in 43.8% of the patients, whereas it decreased in the remaining majority (56.2%). By calculating a "coefficient of variation" (both decrease and increase) in the level of total DNA and non-apoptotic DNA fragments, we compared the values at the beginning and the end of the therapy. For total DNA, the range was between 1.02- and 26-fold (mean 3.76-fold), whereas for non-apoptotic fragments it ranged from 1.01- to 73-fold (mean 6.9-fold) (p=0.033). In accordance with these findings, the integrity of serum DNA was higher in patients with increasing DNA levels and vice versa.
Conclusions: Our findings suggest that non-apoptotic fragments contribute to a higher degree to the change of the DNA level during adjuvant chemotherapy.