Evaluation of circulating cell-free DNA and its integrity as a potential predictive biomarker of breast cancer onset: A pilot study

Background: Although mammographic screening for breast cancer (BC) has substantially increased the rates of detection of early-stage BC, a significant proportion of patients continues to be diagnosed in locally advanced or metastatic settings. The early BC diagnosis is of utmost importance for long-term survival, improving the quality of life and reducing costs for public healthcare. New BC screening approaches integrated with the radiological ones, could improve the early identification of BC, offering more personalized monitoring and treatments. Cell-free DNA (cfDNA) is considered a new potential biomarker for cancer, whose importance has been gradually deepened thanks to the rapid improvement of molecular technologies. As reported in the literature, cfDNA can play an important role in the diagnosis, treatment, and prognosis of many tumors, and it could replace tissue biopsy with a simple blood test. To further understand the value of cfDNA in BC, we used the digital droplet PCR (ddPCR) to investigate ALU and LINE sequences in cfDNA as potential biomarkers for BC diagnosis. Methods: Peripheral blood specimens (12 ml) were collected from 99 patients with primary BC before surgical treatment and from 103 healthy women selected as a control group. The study was approved by the Ethical Committee and informed consent was obtained from all participants. DdPCR was developed to detect cfDNA abundance of long and short fragments, targeting two repetitive DNA elements: ALU (ALU-260 bp, ALU-111 bp) and LINE1 (LINE1-266 bp, LINE1-97 bp). The cfDNA integrity (cfDI) was obtained from the ratio of longer/shorter fragments. Receiver operating characteristic (ROC) analysis was carried out to assess the discriminatory power of cfDI between cases and controls and the area under the curve (AUC) was calculated with 95% confidence interval (95%CI). Results: Patients with BC had a significantly lower cfDI (median ALU = 0.08, median LINE1 = 0.19) compared to the control group (median ALU =0.10, median LINE1 = 0.27) (P < 0.001 for each). ROCanalysis revealed that cfDI allow to distinguish patients with BC from healthy women with an AUC of 0.66, 95%CI: 0.59–0.73 for ALU and 0.78, 95%CI: 0.71–0.84 for LINE1. Comparing AUC curves, we found that the LINE1 marker has a more significant diagnostic performance than ALU (p = 0.005, De-Long Test). Conclusions: The LINE1- cfDI seems to be a stable predictive marker of early BC detection. Although our results need to be further confirmed in a larger and independent cohort, the measurement of LINE1-cfDI with ddPCR may become a suitable predictive strategy. It could be integrated into a screening program to detect early BC and maybe to monitor women with a higher risk for BC. Furthermore, LINE1-cfDI detection by ddPCR could be very useful to monitor BC relapse due to the high sensibility, specificity and reproducibility of the technique. No conflict of interest.