Just in time to raise awareness during National Colorectal Cancer Awareness Month, a new study in the New England Journal of Medicine reports that a blood test has now been developed to detect the presence of colorectal cancer, becoming another tool to identify what has been described as the second leading cause of cancer deaths in the United States. To many, the possibility of a blood test to detect colorectal cancer is a huge development, given that over 150,000 people will be diagnosed with colorectal cancer this year and cases of this cancer are rising at a worrisome rate among people under 50. It’s not clear what’s causing this uptick, though it may have to do with environmental exposures, including food, beverages, and air. Early detection of colorectal cancer means that patients could have over a 90% chance of being cured, but the key is early identification, which means early and regular screening. And that’s what has been a problem.

The “gold standard” for detecting and even preventing colorectal cancer is the colonoscopy, which can discover signs of colorectal cancer in the large intestine and rectum and can even locate pre-cancerous polyps that can then be removed before becoming cancerous. While for those at regular risk, a colonoscopy is generally only recommended once every 10 years, it requires an invasive exam, a day’s prep beforehand, a companion to accompany you home, and possible use of anesthesia. For many, setting aside that much time and effort (plus the expense if you lack insurance) is just not possible or desirable, not to mention the unpleasantness of it. Thus, it’s estimated that 1 in 3 adults over 45 are not screened for colorectal cancer as recommended, which equates to over 50 million Americans. Over 53,000 Americans will die of colorectal cancer this year, the majority of whom did not keep up with regular screening. The average age of diagnosis for colorectal cancer among men and women is 66.

Stool tests are another option for the detection of colorectal cancer, which can allow a person to conduct a test completely without leaving home or doing pre-testing prep. Kits that test stool can be obtained through a prescription or even over the counter or online (Amazon sells them) but unlike a colonoscopy, these tests cannot address the formation of cancerous polyps and must be conducted more frequently than the colonoscopy.  Moreover, a positive stool test will then require that you have a colonoscopy to further evaluate and diagnose your situation. Stool tests are also not as sensitive as colonoscopies, meaning that they may only pick up the presence of a cancerous polyp about 40-70% of the time, as opposed to a rate of detection of up to 95% from a colonoscopy.

So now, with the likely introduction of a blood test, there will be a third option for detecting colorectal cancer, but again with less sensitivity than the colonoscopy. This new blood test is called the Shield test, and it was developed by Guardant Health. It can detect colorectal cancer at Stages 2 or later with 100% sensitivity, but for earlier cancers (with higher cure rates) or even pre-cancerous polyps, its detection is not nearly as sensitive. For stage 1 cancer, the Shield test had a sensitivity rate of 65%. Just as with the stool test, a positive result on this new blood test will then require you to get a follow-up colonoscopy. It’s not yet clear how frequently this blood test will be recommended or how much the test will cost, though it is likely the blood test will be covered by insurance and will receive FDA approval later this year, leading to widespread availability. While some experts are concerned that this blood test might supplant the more sensitive colonoscopy (which can actually prevent colon cancer), it may nonetheless mean that millions more are tested than is currently happening, ultimately leading to fewer colorectal cancer deaths. As other experts make clear, the best colorectal screening test is the one that people will use, whichever one that is. Given that 1 in 3 adults over 45 are currently not getting screened, that may be the best news yet.