Test promises to detect cancer early – before symptoms
/The Food and Drug Administration has not approved them yet, but companies are developing new tests to detect cancer early – when it is most treatable.
These tests, called multicancer detection assays (MCDs) or multicancer early detection tests (MCEDs), are different than current blood tests because they detect early-stage cancer, when the number of tumor cells is still small.
The goal to develop a single test that can identify a variety of cancers early is part of the Cancer Moonshot, the White House’s $1.8 billion federal initiative to reduce cancer death rates and improve the quality of life for cancer survivors.
Cancer screening tests that are commonly available now – including PSA tests for prostate cancer, mammograms for breast cancer, or colonoscopies for colon cancer – can be expensive and uncomfortable for patients. MCDs are meant to make cancer screening easier and more precise.
MCD tests work by looking for trace amounts of tumor DNA in the bloodstream. All cells in the body shed DNA into the bloodstream when they die. This circulating “cell-free” DNA contains information about the tissue it came from and whether it is normal or cancerous. MCD tests look for the trace amounts of tumor DNA in the bloodstream.
A recent article by Colin Pritchard, professor of Laboratory Medicine and Pathology at the University of Washington, explores the potential of such tests – and discusses their potential. Pritchard makes clear that no MCD test is currently approved by the FDA or recommended by medical groups.
However, he said at least one MCD test is available. The Silicon Valley biotech company GRAIL launched the first commercially available test in the U.S. in 2021. The Cleveland Clinic reported on the company’s Galleri test in April. Galleri claims to detect more than 50 different types of cancers.
At least three other companies, Exact Science of Madison, Wisconsin, Singlera Genomics of LaJolla, California, and Freenome of San Francisco, are developing tests.
However, none of these tests are covered by insurance, something more likely to happen once the tests are approved by the FDA. Meanwhile, GRAIL’s Galleri screening costs $949, which you must pay out of pocket.
While the promise is great, there is a concern that MCD tests may result in overdiagnoses of low-risk cancers that are better left undetected. This problem occurred with prostate cancer screening when PSA tests were introduced. That is why medicine has developed nuanced guidelines about who should be screened and when the tests should be done.
Realistically, MCD tests will come into common usage soon. Clinicians will learn more sophisticated and nuanced approaches to prescribing the tests and interpreting their results. No doubt, there will be some overdiagnosis. But the potential to save lives by identifying cancer early will be too appealing to pass up.
We look forward to a future in which we take fuller advantage of the medical advances being achieved.