Blood tests that claim to find many cancers

One blood sample is checked for signs that a cancer may be growing somewhere in the body. Some tests, Galleri for example, look for many cancer types at once, including some, like pancreatic and ovarian cancer, that have no regular screening test. A positive result means more tests are needed to find out whether there is a cancer, and where.

None of these tests covers every type of cancer, and they can miss cancers, early ones included. A negative result doesn’t rule cancer out, and expert groups still recommend the usual screening tests whether or not you have one.

A positive result may turn out not to be cancer. Finding that out can take several scans and sometimes a biopsy, and those tests carry risks of their own.

In the United States, insurance usually doesn’t cover it and a test costs around 900 US dollars. Follow-up tests after a positive result can cost more.

No medical society recommends them for screening, and neither does the US Preventive Services Task Force. The US National Cancer Institute says nobody knows yet whether they do more good than harm. Trials are needed to find out.