Distinguishing Circulating Tumor from Normal Cell-Free DNA

Fragments of circulating DNA from tumors are around 20 to 30 base pairs shorter than those from healthy cells, researchers report.

Jul 19, 2016
Alison F. Takemura

Untreated glioblastoma WIKIMEDIA, AFIPPieces of tumor DNA circulating in the bloodstream are generally shorter than circulating DNA fragments derived from healthy cells, scientists reported this week (July 18) in PLOS Genetics.

Researchers from the University of Washington and the University of Utah observed the DNA difference by analyzing fragments derived from human glioblastoma and hepatocellular carcinoma cells transplanted in rats. The team observed that the human circulating tumor DNA was typically 134 to 144 base pairs long, while the rat circulating DNA was typically 167 base pairs long. 

The scientists were then able to confirm this length difference in people: a cohort of 15 patients with lung cancer compared against nine healthy individuals, GenomeWeb reported.

Human circulating tumor DNA “was overall consistently shorter than the fragment length of normal cell-free DNA,” the authors wrote in their paper.

The findings could help improve cancer diagnosis and treatment prescription using liquid biopsies—a minimally invasive cancer detection method that has some notable limitations, including assay sensitivity.

“This development has the potential to enable earlier detection of solid tumors through a simple blood draw by substantially improving our ability to detect very low quantities of circulating DNA derived from tumor cells,” study coauthor Hunter Underhill of the University of Utah said in a statement.