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Blood tests could predict survival odds for patients with metastatic cancer

As cancers grow and potentially spread to new parts of the body, they often shed cells and DNA into the blood stream. DNA can be analyzed for both the amount of DNA present and whether any potential mutations exist that may aid providers in deciding on treatments.

These tests, known as liquid biopsies, have become standard practice for certain types of cancer, especially those for which there are drugs that target distinct DNA mutations. Whether liquid biopsies could help providers understand which patients may do better than others, though, is unknown.

DNA found in the blood may also be from normal cells. Measuring the amount of DNA that’s been shed by a tumor compared to the body’s typical amount of DNA, defined as the tumor fraction, may be a new tool to predict survival and guide treatment discussions for patients whose cancer has spread from the breast, prostate, lung or colon, a new study finds.

When tumor DNA made up at least 10% of the DNA in the bloodstream of patients with metastatic cancer, researchers discovered, those patients were much less likely to survive than those with less tumor DNA in the bloodstream, across all cancer types studied.

The measurement was just as accurate when it looked at patients with metastatic breast or lung cancer who had less than 1% of tumor DNA in their bloodstreams; these patients had a better chance of living longer than patients with more tumor DNA in the bloodstream.

“There are two reasons to look at anything analytically like this in a patient’s tumor,” said first author Zachery Reichert, M.D., Ph.D., a clinical associate professor and medical oncologist who specializes in urologic oncology at the University of Michigan Health Rogel Cancer Center. “One is it tells you what to do next. The other is it can help you counsel a patient on what to expect.”

“In several cancers, we have multiple options for treatment without knowing which one is better for whom,” he continued. “A better understanding of the disease risk will help the patient and provider better balance the treatment risks.”

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