Cancer stage-dependent alterations in cell-free DNA in patients with colorectal cancer.

Purpose: Cell-free DNA (cfDNA) in plasma is a useful resource for liquid biopsy. The concentration and integrity of cfDNA may be clinical informative for detecting and predicting cancer progression.

Methods: Plasma from 40 healthy controls and 90 colorectal cancer patients was assessed. qPCR targeting the arithmetic-logic unit (Alu) repeats were performed using two different sets of primers amplifying the long and short segments. DNA integrity was calculated by the ratio of the long to the short fragments of amplified Alu repeats.

Results: cfDNA concentration was significantly higher in the patients than that in healthy controls. Patients with stage III colorectal cancer showed no significant difference in their cfDNA levels as compared with the healthy controls. In colorectal cancer, cfDNA level of stage IV patients was higher than that of stage 0-III (p=0.049). The DNA integrity was significantly lower in patients with stage I and II cancer than that in normal controls (p=0.007, 0.029 respectively). The receiver operating characteristic (ROC) curve for discriminating patients with colorectal cancer from normal controls had an area under the curve of 0.672 (95%CI, 0.572 to 0.772) and cfDNA concentration increased within 21 days following surgery and dropped by 3 months after surgery.

Conclusion: Concentration of cfDNA is a promising molecular marker for assessing colorectal cancer progression. Both the cfDNA concentration and its integrity are highly variable. Some cancer stage dependent changes were observed, which warrants further investigation with more patients included.