THURSDAY, March 14 (HealthDay News) -- Circulating tumor DNA is a better biomarker of metastatic breast cancer than cancer antigen 15-3 (CA 15-3) or circulating tumor cells, according to a study published online March 13 in the New England Journal of Medicine.

Sarah-Jane Dawson, Ph.D., of the University of Cambridge in the United Kingdom, and colleagues compared radiographic images of tumors in 30 women with metastatic breast cancer to a circulating tumor DNA assay, CA 15-3, and circulating tumor cells. Circulating tumor DNA was analyzed from serially collected plasma specimens using targeted or whole-genome sequencing. Measurement of CA 15-3 and quantification of circulating tumor cells occurred at the same identical time points.

The researchers found that 29 of 30 cases were detected from circulating tumor DNA. CA 15-3 identified 21 of 27 women and circulating rumor cells detected 26 of 30 women. Greater dynamic range was seen with circulating tumor DNA levels, which correlated better to changes in tumor burden than did CA 15-3 or circulating tumor cells. Circulating tumor DNA provided the earliest of the three measures of treatment response (10 of 19 women).

"This proof-of-concept analysis showed that circulating tumor DNA is an informative, inherently specific, and highly sensitive biomarker of metastatic breast cancer," the authors write.

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