Circulating tumor DNA as a new biomarker

This trial investigated the significance of circulating tumor DNA as a biomarker for monitoring response to treatment among metastatic breast cancer patients. 

The management of metastatic breast cancer requires frequent monitoring of response to treatment in order to avoid ineffective therapies and prevent unnecessary side effects. Normally, cancer response to therapy is monitored by imaging tests or the levels of certain biomarkers (molecules detected by blood test, whose levels indicate the extent of the cancer within the body). However, both radiographic imaging and the commonly used breast cancer biomarker cancer antigen 15-3 (CA 15-3) have demonstrated limited accuracy in previous studies.

Circulating tumor DNA (fragments of the tumor's genetic material) is currently being investigated as a possible new biomarker used to assess tumor extent (often referred to as tumor burden) and response to treatment.

30 women with metastatic breast cancer and undergoing treatment were included in this study. Circulating tumor DNA, as well as CA 15-3 levels and the number of circulating tumor cells (another commonly used biomarker) were assessed and followed throughout treatment. Circulating tumor DNA showed the greatest sensitivity to tumor burden. Circulating tumor DNA was successfully detected in 97% of women, compared to CA 15-3 which was detected in 78% of women, and circulating tumor cells which were detected in 87% of women.

Circulating tumor DNA levels also showed a greater correlation with changes in tumor burden throughout treatment compared to CA 15-3 or circulating tumor cells. Among women with a progressing disease despite treatment, circulating tumor DNA levels increased in 89% of women, compared to 37% of women showing an increase in circulating tumor cells and 50% showing an increase in CA 15-3 levels. In addition, increasing levels of circulating tumor DNA were also found to be associated with inferior overall survival.

This study concluded that circulating tumor DNA can provide an accurate assessment of tumor burden and response to treatment among metastatic breast cancer patients. 

This study included only a very small number of participants. Larger studies examining the prognostic significance of circulating tumor DNA are awaited.