Nocturnal increase of concentration of circulating tumor DNA in metastatic colorectal cancer patients with disease control but not with progressive disease

The utility of liquid biopsy in clinical oncology is often compromised by low concentration of tumor-derived fragments. Recent study demonstrated a nocturnal peak in the amount circulating tumor cells during the deep sleep phase (~ 4 a.m.). This study questioned whether the same peak is characteristic of circulating tumor DNA (ctDNA).Plasma samples were collected from 19 RAS/RAF-mutated colorectal cancer (CRC) patients at 12 p.m. (day 1), 4 a.m. (night), and 12 p.m. (day 2). 14 subjects provided a single triplet for the study, and 5 patients underwent the above procedure twice or thrice. KRAS, NRAS , and BRAF mutations in plasma were quantified via ddPCR. RAS/RAF mutations (> 10 copies/mL) were detected in at least one plasma sample in 20/25 (80%) triplets. Among these, 15 showed detectable ctDNA at all timepoints, with intra-individual variation ranging from 1.7% to 74.8%. In five triplets, ctDNA was undetectable during daytime but present at night. Overall, 7 of 9 triplets collected at the time of disease control exhibited a night peak in ctDNA concentration, while all 10 triplets obtained during tumor progression showed other patterns of ctDNA changes (p = 0.005, Fisher’s exact test).These findings demonstrate that ctDNA level is a subject of circadian variations in a subset of cancer patients.