Detecting cancer early before it spreads throughout the body can be lifesaving. This is why doctors recommend regular screening for several common cancer types, using a variety of methods. Colonoscopies, for example, screen for colon cancer, while mammograms screen for breast cancer.
While important, getting all these tests done can be logistically challenging, expensive and sometimes uncomfortable for patients. But what if a single blood test could screen for most common cancer types all at once?
This is the promise of multicancer early detection tests, or MCEDs. This year, President Joe Biden identified developing MCED tests as a priority for the Cancer Moonshot, a US$1.8 billion federal effort to reduce the cancer death rate and improve the quality of life of cancer survivors and those living with cancer.
As a laboratory medicine physician and researcher who develops molecular tests for cancer, I believe MCED tests are likely to transform cancer screening in the near future, particularly if they receive strong federal support to enable rapid innovation.
How MCED tests work
All cells in the body, including tumor cells, shed DNA into the bloodstream when they die. MCED tests look for the trace amounts of tumor DNA in the bloodstream. This circulating “cell-free” DNA contains information about what type of tissue it came from and whether it is normal or cancerous.
Testing to look for circulating tumor DNA in the blood is not new. These liquid biopsies – a fancy way of saying blood tests – are already widely used for patients with advanced-stage cancer. Doctors use these blood tests to look for mutations in the tumor DNA that help guide treatment. Because patients with late-stage cancer tend to have a large amount of tumor DNA circulating in the blood, it’s relatively easy to detect the presence of these genetic changes.
Scientists are using strands of DNA that circulate in the blood as a way to detect early-stage cancer.
MCED tests are different from existing liquid biopsies because they are trying to detect early-stage cancer, when there aren’t that many tumor cells yet. Detecting these cancer cells can be challenging early on because noncancer cells also shed DNA into the bloodstream. Since most of the circulating DNA in the bloodstream comes from noncancer cells, detecting the presence of a few molecules of cancer DNA is like finding a needle in a haystack.
Making things even more difficult, blood cells shed abnormal DNA naturally with aging, and these strands can be confused for circulating cancer DNA. This phenomenon, known as clonal hematopoiesis, confounded early attempts at developing MCED tests, with too many false positive results.
Fortunately, newer tests are able to avoid blood cell interference by focusing on a type of “molecular barcode” embedded in the cancer DNA that identifies the tissue it came from. These barcodes are a…
