Prospective study of quantitation of plasma DNA levels in the diagnosis of malignant versus benign prostate disease

Purpose: The aim of this study was to determine the potential of cell-free DNA levels as a diagnostic marker for prostate cancer, having first established the effect that blood sample processing has on this measurement. Experimental Design: A total of 152 blood samples were collected prospectively from patients before their prostate biopsy and 25 from men in two distinct control groups. Blood was processed to yield three components: one-spin plasma (n = 68), two-spin plasma (n = 152), and serum (n = 56) samples. Results: Having established the effect of sample preparation on the measured DNA level, the more reliable two-spin plasma sample was used to determine the relationship between the DNA level and the presence of prostate cancer. Those patients with cancer (n = 78) had a significantly higher level of DNA compared with the control groups (P < 0.0001 and P < 0.0001). However, DNA levels in patients with a benign biopsy (n = 74) were significantly higher than the 78 patients confirmed to have cancer (P = 0.02). Conclusions: We conclude that the sample type used in the quantitation of cell-free DNA has an effect on the level reported. Elevated levels are present in the two-spin plasma samples of patients with prostate cancer compared with healthy controls but are not of diagnostic value during the management of prostate cancer.