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New blood test could predict breast cancer relapse risk

Weeks or even months before there is evidence of a tumor in scans or biopsies, a simple blood test could detect the risk of relapse in survivors of early stage breast cancer.

The "liquid biopsy" developed at the Institute of Cancer Research in London is a kind of blood test that shows promise in detecting cancer DNA in the blood before the cells grow into tumors. The results of a prospective pilot study of the test were published Wednesday in the journal Science Translational Medicine.

Using a technique called mutation tracking, researchers say the blood test identified the risk for relapse an average of 7.9 months before traditional biopsies or imaging scans would have shown tumors, referred to as clinical relapse.

"By tracking that, we can see whether after surgery there is disease present in that patient that we couldn't actually detect with our normal imaging approaches," Professor Mitch Dowsett of the Institute of Cancer Research and The Royal Marsden NHS Foundation Trust told CBS News. "It's far more sensitive and it's actually very specific."

Researchers say the blood test they developed can detect an individual's specific "circulating tumor DNA," or ctDNA, matched to the cancer for which they were treated. Previous research has also indicated that mapping cancer DNA could be one of the keys to earlier disease detection.

In this study, the team followed a 55 English women who were diagnosed with early stage breast cancer, then treated with both surgery and chemotherapy. They monitored ctDNA in the women's blood tests after surgery and every six months using the DNA profiles of each individual's specific pre-treatment cancer cells. In 54 of the 55 women, researchers were able to accurately predict relapse risk based on ctDNA levels.

Breast cancer is the most commonly diagnosed cancer among women, aside from skin cancers, and the second most deadly cancer in women. The study says 95 percent of women diagnosed have early stage breast cancer that doesn't appear to have spread. After treatment, there can be undetected, residual cancer cells.

"This new technique will allow us to begin to measure whether or not that disease is coming through before it actually reveals itself," Dowsett said.

Building on these results, the team plans a larger study next year. It could be a few years before the blood tests are widely available to cancer survivors.