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.

According to the Associated Press, the cost isn't covered by most insurance plans and the tests haven't been endorsed by medical groups or recommended by U.S. health authorities.

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

The AP reported that the experiment could last seven years and have 200,000 participants.

But there have been cancer tests in the past after studies found they didn't save lives.

A study in Japan on cancer screening for infants in 2004 and a 16-year ovarian cancer screening study of 200,000 women in the U.K. were both halted after studies found they didn't save lives, the AP reported.