Preferred end coordinates and somatic variants as signatures of circulating tumor DNA associated with hepatocellular carcinoma.

Circulating tumor-derived cell-free DNA (ctDNA) analysis offers an attractive noninvasive means for detection and monitoring of cancers. Evidence for the presence of cancer is dependent on the ability to detect features in the peripheral circulation that are deemed as cancer-associated. We explored approaches to improve the chance of detecting the presence of cancer based on sequence information present on ctDNA molecules. We developed an approach to detect the total pool of somatic mutations. We then investigated if there existed a class of ctDNA signature in the form of preferred plasma DNA end coordinates. Cell-free DNA fragmentation is a nonrandom process. Using plasma samples obtained from liver transplant recipients, we showed that liver contributed cell-free DNA molecules ended more frequently at certain genomic coordinates than the nonliver-derived molecules. The abundance of plasma DNA molecules with these liver-associated ends correlated with the liver DNA fractions in the plasma samples. Studying the DNA end characteristics in plasma of patients with hepatocellular carcinoma and chronic hepatitis B, we showed that there were millions of tumor-associated plasma DNA end coordinates in the genome. Abundance of plasma DNA molecules with tumor-associated DNA ends correlated with the tumor DNA fractions even in plasma samples of hepatocellular carcinoma patients that were subjected to shallow-depth sequencing analysis. Plasma DNA end coordinates may therefore serve as hallmarks of ctDNA that could be sampled readily and, hence, may improve the cost-effectiveness of liquid biopsy assessment.
Competing Interests: Conflict of interest statement: The authors declare a conflict of interest. K.C.A.C., R.W.K.C., and Y.M.D.L. hold equities in Grail. P.J., K.C.A.C., R.W.K.C., and Y.M.D.L. are consultants to Grail. K.C.A.C., R.W.K.C., and Y.M.D.L. receive research funding from Grail. Y.M.D.L. is a scientific cofounder of and serves on the scientific advisory board of Grail. P.J., K.C.A.C., R.W.K.C., and Y.M.D.L. have filed patent applications based on the data generated from this work. Patent royalties are received from Grail, Illumina, Sequenom, and Xcelom.
(Copyright © 2018 the Author(s). Published by PNAS.)