Screen for colon cancer

Screening for colorectal cancer isn’t exactly something most people look forward to. It can be uncomfortable, invasive and time-consuming. No wonder 1 in 3 people who should get tested have never received any screening, according to the American Cancer Society.

Yet this is essential care, as it can detect cancer when it is in its early stages and easier to treat. In fact, colorectal cancer is the second-most-common cause of cancer death in the United States. More than 53,000 Americans are expected to die of it this year alone.

Here’s the good news: A new blood test might soon offer a more convenient way for people to get tested. Though it is not as effective at detecting cancers and precancerous polyps as colonoscopy, it can be a valuable tool for individuals who otherwise would put off testing.

Most Americans are recommended to start receiving colon cancer screenings at age 45 and to keep doing so regularly until they reach at least 75. (People at higher risk of colon cancer might need to begin earlier and receive them more frequently.) There are two types of approved methods: One is through visual inspection of the colon and rectum, via colonoscopy, CT colonography or sigmoidoscopy.

Colonoscopy, recommended every 10 years, requires a gastroenterologist to pass a long tube through the patient’s bowels. Those undergoing the procedure must first clean out their colon with laxatives and generally are put under anesthesia during the procedure.

Sigmoidoscopy is quicker, offers a more limited view of the bowels, but also usually requires laxatives and light sedation. It can be done in lieu of colonoscopy every five years, as can the CT colonography, which involves bowel preparation — but no sedation.

The second type of approved method is stool-based tests. Patients collect a fecal sample at home and then send the sample to a lab. The lab then looks for characteristics, such as blood or tumor DNA, that could suggest cancer. Depending on the test, screening should be done every one to three years.

Colonoscopy is the most accurate screening method. It also offers the advantage of being a preventive tool, since gastroenterologists can remove polyps that they find during the procedure. Many polyps never turn into cancer, but some do. Identifying and removing them early prevent them from developing into tumors later.

Despite the ready availability of these tests, as many as 50 millions Americans are not upto-date. The prospect of bowel cleansing and sedation might be off-putting to some. Others could be squeamish about manipulating their own stool.

Then, of course, there are those who do not have a specific reason but have delayed doing it because they have too much else on their plates.

Here’s where a blood test offers substantial value. Imagine if, at your annual physical, your doctor could simply add a blood test for colon cancer to the slew of tests you are already receiving. This would require no additional work from the patient and would almost certainly increase screening rates.

The test, called Shield, looks for tumor DNA that is shed into the bloodstream. A study published last month in the New England Journal of Medicine found that the method detected more than 87 percent of early-stage cancers. The false positive rate was about 10 percent, meaning that 10 percent of people who tested positive turned out not to have cancer upon further examination.

These promising results are on par with the accuracy of fecal tests. But there is at least one major limitation: Though Shield appears very good at finding cancers, it does not pick up most large polyps that could be precancerous. In fact, it detects just 13 percent of polyps that could develop into cancer. By comparison, fecal tests pick up more than 40 percent of them, and colonoscopies find up to 93 percent (and can result in them being immediately removed).

The Food and Drug Administration has not yet approved Shield, though based on the new results, I anticipate the agency will soon. Major medical organizations would then weigh in on how it could be incorporated into existing screening guidelines.

Among the questions they should consider is whether this tool should be recommended to younger adults who might hesitate to receive screenings. Though the incidence of colon cancer and death from the disease have been trending down overall, diagnoses among young people have been rising.

In 1995, 11 percent of colorectal cancer cases were among people 55 or younger; by 2019, that number had risen to 20 percent. The proportion of younger people diagnosed in advanced stages also increased, from 52 percent in the mid2000s to 60 percent.

In the meantime, people should follow cancer screening guidelines and begin either direct visualization methods or fecal tests at age 45. Those with a family history of colon cancer should speak with their health-care providers about whether they should begin even earlier. Nearly 70 percent of colorectal cancer deaths can be prevented if everyone gets screened regularly. Eligible people should not delay.