A new blood test can help predict if melanoma survivors will have a future bout with skin cancer, researchers say.

The test looks for DNA fragments that are shed by tumors and float free in a person’s bloodstream.

About 80% of later-stage melanoma patients who had detectable levels of these DNA fragments before cancer treatment later had their skin cancer recur, researchers reported April 15 in The Lancet Oncology.

In fact, skin cancer returned more than four times faster in this group than in melanoma patients with no detectable DNA fragments, researchers said.

What’s more, the higher their levels, the faster their cancer returned, results revealed.

“Our findings suggest that circulating tumor DNA tests could help oncologists identify which melanoma patients are most likely to respond well to therapy,” lead investigator Mahrukh Syeda said in a news release. Syeda is a research scientist in dermatology with the NYU Grossman School of Medicine in New York City.

“In the future, such assessments may be used routinely in the clinic to help guide treatment decisions,” Syeda said.

For the study, researchers analyzed blood samples taken from nearly 600 men and women who were part of a previous clinical trial for advanced melanoma.

In stage 3 disease, cancer cells have spread from the skin to nearby lymph nodes. After the lymph nodes are removed as part of treatment, it can be hard to spot whether a person’s cancer is coming back, researchers said.

Results showed that detectable levels of tumor DNA fragments did indeed predict the likelihood of skin cancer recurrence.

Researchers also found that patients with detectable levels of DNA fragments during their treatment — at three, six, nine or even 12 months into cancer therapy — were more likely to have melanoma come back.

DNA fragments found in the bloodstream during treatment could mean that a patient’s cancer is getting worse, researchers said.

These results indicate that this blood test is as good or better at predicting melanoma recurrence as other experimental tests based on factors like the immune activity of cancer cells, researchers said.

“Unlike standard, tissue-based analyses of tumor cells, which can only suggest the likelihood of recurrence, circulating tumor DNA tests provide a clear, direct measure of the disease itself and can tell us outright that melanoma has returned,” senior researcher Dr. David Polsky, a professor of dermatologic oncology with the NYU Grossman School of Medicine, said in a news release.

Next, researchers plan to improve the test and see whether it can help make better treatment decisions for melanoma patients.