Liquid Biopsies for Cancer Screening

There have been recent news reports about the development of blood tests that may be able to find some cancers long before other screening methods could help. On the one hand, this feels like the magic bullet of cancer prevention/screening; while, on the other, it clearly could be very complicated and result in unnecessary worries or false positives.

Called liquid biopsies, such blood tests are being advertised as a way to possibly find teeny cancers in otherwise healthy people.

Called liquid biopsies, such blood tests are being advertised as a way to possibly find teeny cancers in otherwise healthy people. We know that cancer cells shed DNA fragments into the blood, and these tests may detect such markers.

Especially in types of cancer that have no other good screening (think pancreas, stomach, or ovary), these sound potentially extremely helpful. President Biden has announced an initiative to reduce the cancer death rate in the United States by 50% over the next 25 years, and this might be a way to move towards that goal.

A California-based company, Grail, is advertising the tests for slightly under $1,000. Most insurance companies don’t cover the cost, and most scientists and physicians say that we just don’t know enough to know if these tests are valuable and can save lives.

At the moment, no major medical groups or government health authorities have endorsed them. The Food and Drug Administration (FDA) does not have the same kind of requirements for a blood test as they do for drugs. That is to say, this is all perfectly legal and falls into the usual requirements of our open market.

You are probably aware of another advertised test with a similar goal. Although not covered by insurance, it is possible to have a full body CT scan with the focus on finding unknown, undiagnosed, small cancers.

These scans have not been very effective in finding cancers in healthy people. Like the blood tests, they are not recommended by any medical group or government agency. They find cancer in less than two percent of all people who undergo them, and some of these cancers would never cause a problem if left undetected.

They can also miss things. Mammograms, for example, are much better at identifying early signs of breast cancer. Finally, they use a lot of radiation, and it is generally wise to avoid unnecessary exposure.

There have been other experiences with highly touted cancer screening tests that turned out not to be useful. In 2004, a Japanese study that was testing all infants for a childhood cancer was stopped because it did not save lives. In 2021, a 16-year-long study in the United Kingdom found that regular screening of healthy women for ovarian cancer made no difference in the death rate from that illness.

Screening can find cancers that, if left alone, would never be threatening and likely never even found. There are also some aggressive cancers that are lethal no matter how early they are discovered.

These blood tests are not diagnostic. What they may do is find cancer fragments in blood and trigger a series of scans and other tests to try to find the cancer. Think of the anxiety experienced when a questionable mammogram finds something that needs to be biopsied. This is a similar situation on steroids.

The blood test gives few hints of even where to search for a malignancy, and, if there indeed is a cancer growing, it may still be too small to show up on a scan or MRI. What then?

We all applaud the efforts to improve cancer screening and to develop tests that are effective. Unfortunately, we’re not there yet.