Balancing hope and reality: The promise and peril of blood-based colorectal cancer screening

As a gastroenterologist and cancer researcher, my mission is to help my patients live longer, healthier, and cancer-free lives. A rise in the number of younger Americans diagnosed with colorectal cancer worries me — early-age onset colorectal cancer is expected to surge by more than 140% by 2030. But because colorectal cancer is preventable with early screening and detection, it’s possible to reduce the number of Americans diagnosed with this disease in the prime of their lives.

The New England Journal of Medicine recently published a pivotal paper that found a blood test can detect the early stages of colorectal cancer, which is one of a handful of cancers that is increasing every year in Americans younger than age 50.

That a simple blood test can replace an invasive colonoscopy sounds amazing. Not so fast. Medical innovations give hope, but new technologies meant to save lives risk making the current crisis worse if they aren’t introduced with care.

On one hand, blood-based screening is great for access: individuals would no longer need to take a day off work for a colonoscopy and take a couple days for the laxative prep, or manipulate their own stool as at-home tests require. Letting primary care providers order a simple blood test could make it easier for people who are hesitant, too busy, or physically unable to get colonoscopies to be checked for colorectal cancer. Ultimately, this could help reduce disparities in screening uptake and close the serious equity gap in colorectal cancer incidence and mortality.

On other hand, the use of blood-based tests fundamentally shifts the approach to controlling this deadly disease away from prevention and toward detection. Blood-based screening tests can only tell you if you already have developed colorectal cancer, but they cannot help you prevent it from occurring in the first place.

Colonoscopies are a powerful tool to help identify and remove precancerous polyps as well as identify cancer early when it is in the most treatable stages. In fact, studies published by the American Gastroenterological Association show that colonoscopies decrease new colorectal cancer cases and deaths by 69% and 89%, respectively. That’s why colonoscopies must remain the gold standard of care and why blood tests must complement them, not replace them.

Despite progress since the 1990s, colorectal cancer is still the nation’s second deadliest form of cancer. And it is becoming much more common among people in the prime of their lives. This is a major reason why the recommended age to get a colonoscopy was lowered to age 45. Early screening, detection, and removal of pre-cancerous polyps can prevent colorectal cancer.

Many people (and even many physicians) may not understand the nuances and limitations of current blood-based tests. A blood test should not be considered a replacement for a colonoscopy. In addition to its inability to prevent cancer, the blood test evaluated in the NEJM study is based on a biological mechanism called methylation that is more common among older people, and no one knows how — or even if — the test would work well for younger people. If people begin flocking to a blood test instead of colonoscopy, I worry that colorectal cancer will be diagnosed at later stages when it becomes less curable and more deadly. That would mean not only more people diagnosed with cancer than with current guideline-recommended screening options, but more cancer surgeries, chemotherapy, treatments, and deaths.

The shift from a focus on prevention to early detection means that more people will hear those dreaded words: “You have cancer.”

Blood-based tests are important to expand options for patients and their physicians in colorectal cancer screening. But tests that both prevent and detect colorectal cancer early should continue to be the encouraged gold standard. After all, it’s better to prevent colorectal cancer before it occurs than catch it afterward.

Folasade P. May, M.D., is a gastroenterologist, director of quality in digestive diseases at UCLA Health, and the diversity, equity, and inclusion editor for the journal Clinical Gastroenterology and Hepatology.