The findings add to the urgency to find reliable ways to detect colorectal cancer early in young people. Most medical groups have for years recommended people start routine screening only at age 50 unless they have specific risk factors, like a family history of the disease or chronic conditions like inflammatory bowel disease that raise the risk. One organization, the American College of Gastroenterology, recommends that African-Americans start routine screening at 45 because they are at higher risk for colorectal cancer than whites.

Any proposal to expand universal screening, however, will be both controversial and potentially costly, since the vast majority of colorectal cancer deaths still occur among older adults.

“I don’t know that this very small uptick in mortality means we ought to start doing colonoscopies on 20-year-olds as a routine matter,” said Dr. Michael Potter, a professor of family and community medicine at the University of California, San Francisco. More lives would be saved by increasing screening at age 50, he said, adding, “It’s worth doing research in this area to determine whether lowering the age of colorectal cancer screening would yield more benefits than harms. These are not risk-free procedures.”

Screening tests are also expensive, though cost is not the driving issue. Looking for colon cancer in young people is like looking for a needle in a haystack — you’d have to screen a lot of people to detect even a small number of cancers or precancerous polyps. Most young people would go through the process for no good reason, and some would sustain injuries or other harms.

Complications from colonoscopy, considered the gold-standard test, are fairly frequent. A study of over 300,000 healthy Medicare patients who had colonoscopies found that nearly 2 percent wound up in an emergency room or hospital within a week of the procedure because of complications such as tears in the wall of the colon or rectum, which can be life-threatening.

But while some organizations specifically state that colonoscopy is the preferred screening method, the United States Preventive Services Task Force endorses a variety of screening tests, including some that are less expensive or noninvasive, though they may not be as effective in finding and preventing cancers. Stool tests that examine fecal samples for microscopic amounts of blood and DNA changes, for example, can indicate the presence of a tumor or polyp, but such tests need to be done more frequently and may have to be followed up with a colonoscopy if the result is positive.

All of the testing options have pros and cons, and some may yield a false positive test, subjecting someone to additional testing for no reason, or a falsely reassuring negative result.