We have previously reported that the amount of circulating cell-free DNA (ccfDNA) decreases after curative resection of liver metastases but increases in patients with relapsing metastatic colorectal cancer (CRC). However, ccfDNA comes from both cancer cells and normal cells, which adversely affects the accuracy of its measurement. Whereas ccfDNA in healthy individuals consists of about 180-bp fragments from apoptotic cells, in cancer patients, ccfDNA of varying lengths is derived from necrotic tumor cells. Therefore, higher levels of long ccfDNA fragments could indicate the presence of tumor cells. Although, physical damage (like inflammation or surgical stress) also releases long fragments. In ccfDNA, ß-globin is known to reflect the degree of physical damage. We thus developed a new biomarker, ccfDNA long fragment/ß-globin Ratio (cLBR), which is calculated by LINE-1 297-bp/ß-globin. In this study, we evaluate the clinical use of cLBR for prediction of early relapse after resection of metastatic liver tumors from CRC.
We enrolled 29 patients who had undergone resections of metastatic liver tumors from primary CRC. Peripheral blood was collected before and 1-month after surgery. We extracted ccfDNA from 1 mL plasma using the QIAamp Circulating Nucleic Acid Kit (Qiagen). We measured LINE-1 297-bp and ß-globin in ccfDNA using real time PCR, and calculated cLBR. Additionally, in patients with KRAS mutations, we measured ccfDNA KRAS copy number using digital PCR. The Ethics Review Committee of our institution approved the study, and each patient provided written informed consent.
Of the 29 patients, we completed 1-year follow-up for 18 patients. Of these 18, relapse was detected in 8 and no signs of relapse were detected in the other 10. In all 8 patients which relapse was detected, cLBR 1-month after surgery increased. Conversely in the 10 patients without relapse, cLBR 1-month after surgery decreased. On the other hand, in patients with KRAS mutation, the change in KRAS mutation copy number did not associate with relapse.
cLBR can be a useful predictor of early relapse in patients after resection of metastatic liver tumors.
Clinical trial identification
Legal entity responsible for the study
Nippon Medical School
Research funding of Department of Digestive Surgery, Nippon Medical School
All authors have declared no conflicts of interest.