(AP) — A new type of blood test that checks for signs of cancer in healthy people has hit the market.

But it’s still unclear whether these screening tests will make any difference in cancer death rates. Such blood tests, called liquid biopsies, are already used in patients with cancer to tailor their treatment and check to see if tumors come back.

Now, one company is promoting its $949 blood test to people with no signs of cancer.

U.S. government researchers are planning a large experiment to see if the blood tests do actually catch cancers earlier and save lives.