Colorectal cancer was once considered primarily a disease of aging. But rates are now on the rise among younger adults. Since 2011, colon cancer rates among people younger than 50 have increased by about 2 percent every year, according to the American Cancer Society (ACS).

That’s why in the last few years, major medical groups, including the ACS and the U.S. Preventive Services Task Force, have said that people should now begin screening for colorectal cancer starting at age 45. Previous guidance had recommended that most people begin screening at age 50.

In 2020, a large analysis published in JAMA Network Open found a sharp increase in colorectal cancers diagnosed at age 50 vs. age 49, suggesting that many people may have had preexisting cancers that were detected when they began screening at age 50. (A senior author of the analysis received money from companies involved in screening.)

Still, the vast majority of cases are found in people older than 50. 

In 1995, 10 percent of cases of colorectal cancer were diagnosed in people younger than 54; by 2019, that number had risen to 20 percent.

Younger people getting these cancers more often was part of what fueled a reexamination of the best age to begin screening, says Andrew Wolf, MD, an associate professor of medicine at the University of Virginia Health System, who chaired the ACS subcommittee that developed its most recent colorectal cancer screening guidelines.

"A 45-year-old today has the same risk of developing colorectal cancer as a 50-year-old did in the 1990s, when we first started recommending that screening begin at age 50," says Wolf. "A 45-year-old should consider themselves 50 when it comes to colon cancer."

Colorectal cancer screening, like most cancer screenings, poses potential downsides along with its benefits. Colonoscopy—the most common screening method—is often an uncomfortable process. And it comes with some limited risks, including small but potentially serious punctures in the colon or rectum called perforations. Other screening tests, such as the FIT test (more on this below), can produce false positives that may lead to unnecessary colonoscopies.

"Screening is always a trade-off with benefit and harm," says Douglas J. Robertson, MD, chief of gastroenterology at the Veterans Affairs Medical Center in White River Junction, Vt., and a professor at the Geisel School of Medicine at Dartmouth College in Hanover, N.H. "The trade-off is that as you go to younger and younger age groups, the absolute risk for getting or dying from cancer is lower, so more and more people would need to be screened to find the one case of colorectal cancer hiding in these younger age groups."

For those reasons, starting colorectal cancer screening at 50 was the norm for a long time. But in recent years, with rising rates of this cancer in younger adults, the norm has shifted. Today, the major professional medical groups that make recommendations on cancer screenings all generally agree that—unlike a decade ago—the benefits of screening now outweigh the risks for adults starting at age 45. 

There are some slight variations on the advice. The American Cancer Society recommends that all average-risk adults begin colorectal cancer screening at 45. The U.S. Preventive Services Task Force gives screening starting at age 45 a “B” grade recommendation, its second strongest, while screening at age 50 earns an “A” grade. The U.S. Multi-Society Task Force on Colorectal Cancer (MSTF), which represents the American Gastroenterological Association and other professionals, says it “suggests” screening for people ages 45 to 49, while it “strongly recommends” screening starting at age 50. 

In spite of those minor differences, most experts agree that more people should be routinely screened for colorectal cancer, which is the second-leading cause of cancer death in the U.S. In 2021, only about 60 percent of adults older than 45 were up to date with screening.

"We certainly feel that if the conversation starts at 45 and people get screened by 50, that would be a huge step forward," says Wolf, chair of the ACS subcommittee.

Ultimately, most experts say, it should be a conversation between doctor and patient that takes an individual’s values and priorities into account.

The ACS guidelines don’t favor any particular screening technique for colorectal cancer, listing several options. (You can read about all of them on the ACS site.)

But the MSTF guidelines take a tiered approach for simplicity, suggesting that patients be presented with two options first—in part to avoid confusion.

Colonoscopy, in which a doctor uses a tube with a small camera attached to examine the inside of your colon, remains the gold standard for colorectal cancer screening in the U.S. During a colonoscopy, a doctor can not only detect cancers of the colon and rectum but also remove precancerous polyps that might develop into cancer. Patients generally must drink a liquid laxative to clean out the colon in advance and undergo sedation for the procedure itself. Those who choose this screening method must be screened every 10 years.

The second tier-one option, the fecal immunochemical test (FIT), must be done annually—and a colonoscopy is required as a follow-up if there’s a positive result. FIT is much simpler and less invasive. Using an at-home kit, patients spread a small sample of stool onto a card and mail it in for testing, which looks for signs of hidden bleeding.

Ultimately, "people should be encouraged to choose the test that they are most likely to do," Robertson says. "The most effective test is the one that gets done." 

People can also take steps to reduce the risk of colon cancer, including quitting smoking, reducing alcohol consumption, cutting back on processed meat, and getting plenty of fiber and whole grains. Screening alone, experts say, is not enough.