Blood test measures tumor DNA to mark breast cancer drug response

Right now, doctors measure a breast cancer patient's response to treatment, in part, through tissue sample biopsies. But work is well under way on a diagnostic test that would accomplish the same task in a less invasive way, measuring the blood for DNA that breaks off from dying tumor cells.

Nature reports on the efforts of the Cancer Research UK Cambridge Institute and others to advance the new diagnostic. Their research, detailed in The New England Journal of Medicine, showed real promise based on a test run of the diagnostic on blood from 30 women suffering from advanced breast cancer.

Researchers were able to spot circulating tumor DNA in 29 of the 30 women. And they found that the measure of circulating tumor DNA correlated much more with tumor levels than biomarkers such as cancer antigen 15-3, or circulating tumor cells. The DNA blood test also worked with a high level of sensitivity.

While success with a proof-of-concept test is noteworthy, a far wider trial will be important to determine if the test is viable. Still, early signs point to the development of a blood test that could offer a much cheaper, more efficient and quicker way to see how far a cancer has metastasized. Such a test can help doctors adjust a treatment accordingly, and serve as a viable, minimally invasive alternative to biopsy.

"It can be very scalable, inexpensive and useful," Massachusetts General Hospital Cancer Center researcher Daniel Haber, who wasn't involved in the study, told Nature.

But there are flaws. For this study, the scientists looked for cancer-associated gene mutations involving primarily TP53 and PIK3CA, according to the article. But not every tumor will have the same markers, and the researchers note in the story that certain patients may require a customized blood test that looks for tumor markers specific to their cancer.

- read the full Nature story
- here's the NEJM  study