Blood test may detect cancer a year before conventional scans

Boston, Mass — Researchers have taken an important step toward better lung cancer treatment by using blood tests to track genetic changes in tumors as they progress from their very earliest stages.

With experimental tests that detect bits of DNA that tumors shed into the blood, they were able to detect some recurrences of cancer up to a year before imaging scans could, giving a chance to try new therapy sooner.

It's the latest development for tests called liquid biopsies, which analyze cancer using blood rather than tissue samples.

Some doctors use these tests now to guide care for patients with advanced cancers, mostly in research settings.

The new work is the first time tests like this have been used to monitor the evolution of lung tumors at an early stage, when there's a much better chance of cure.

Only about one third of lung cancer cases in the United States are found at an early stage, and even fewer in other parts of the world.

But more may be in the future as a result of screening of longtime smokers at high risk of the disease that started a few years ago in the U.S. Early-stage cases are usually treated with surgery.

Many patients get chemotherapy after that, but it helps relatively few of them.

"We have to treat 20 patients to cure one. That's a lot of side effects to cure one patient," said Dr. Charles Swanton of the Francis Crick Institute in London.

The new studies he led suggest that liquid biopsies might help show who would or would not benefit from chemotherapy, and give an early warning if it's not working so something else can be tried.