Monitor tumor burden with circulating tumor DNA.

There is a need to identify better biomarkers to monitor diseases and/or assess therapeutic responses. For those with cancer, one can identify DNA fragments that contain somatic mutations originating in the tumor DNA in plasma or serum. There have been several early studies suggesting that advances in sequencing technologies will allow identification of somatic genomic alterations that can be used to monitor tumor dynamics. Dawson et.al. investigated circulating cell-free DNA carrying tumor specific alterations in patients with breast cancer. The authors compared CT imaging from 30 women with metastatic breast cancer receiving treatment, using two assays for circulating tumor DNA, CA 15-3, and CTCs. Taken the two methods together circulating tumor DNA was detected in 29 or 30 women (97%) and 115 of 141 plasma samples (82%). Circulating tumor DNA levels showed a greater dynamic range and greater correlation with changes in tumor burden than did CA 15-3 or CTC. The relatively small study showed that circulating tumor DNA has a superior sensitivity to other circulating biomarkers and a dynamic range that correlates with tumor burden.