Colorectal Cancer on the Rise in Adults Under 50
In some respects, the U.S. is winning the war on cancer. Recent reports show an overall decline in the number of new cancer cases and fewer cancer deaths.

But those gains aren’t being shared by everyone. A case in point: A new study shows that rates of colon and rectal cancers have climbed in younger adults over the last decade.

That’s happening even as colorectal cancer rates have dropped steadily in adults over 50, the age most people are advised to start screening for the disease.

Researchers aren’t sure what’s causing the increase in younger adults. But they hope their study will raise awareness among younger patients and their doctors, who may dismiss cancer as a cause of their symptoms.

“These young people are getting ignored. They’ve had symptoms for a year or a year and a half before they finally get diagnosed,” says researcher Y. Nancy You, MD, a surgeon at the University of Texas M.D. Anderson Cancer Center in Houston.

Tracking Trends in Colon Cancer

The study looked at nearly 600,000 colorectal cancer cases reported to a national registry between 1998 and 2007.

As expected, cancer was much more common in the older age group. About 89% of the cases were seen in adults over age 50.

But while colorectal cancer cases have dropped steadily in adults over 50, they increased by more than 2% each year in younger adults.

The increase was highest for rectal cancers, which jumped nearly 4% each year. Colon cancer rates rose nearly 3% per year.

To compound the problem, doctors say many people may not suspect cancer when symptoms like bleeding, abdominal pain, or a change in bowel habits strike someone in their 30s or 40s.

“Most young people, when they have these types of symptoms, they are not thinking that they have cancer. Then they go to their physician and the physician isn’t thinking that they have cancer,” says Rebecca Siegel, MPH, an epidemiologist with the American Cancer Society in Atlanta.

The result is often a delay in diagnosis.

Study Projects Significant Increase in Colorectal Cancer Among Young Adults

Despite an overall drop in colorectal cancer incidence since 1998, some researchers are projecting that by 2030, the incidences of colon and rectal cancers among adults ages 20-34 will increase by 90 percent and 124 percent, respectively, and by 28 percent and 46 percent, respectively, among those ages 35-49. That was the conclusion of a study(archsurg.jamanetwork.com) published online Nov. 5 in JAMA Surgery, which found the incidence of colorectal (CRC) cancers in these age groups is on the rise.

This increase is in marked contrast to the 30 percent decline in colon cancer incidence in adults older than 50 that occurred from 2000 to 2010, said family physician Richard Wender, M.D., who is chair of the National Colorectal Cancer Roundtable and chief cancer control officer for the American Cancer Society.

“The decline in Americans over 50 is very likely entirely due to steadily increasing colon cancer screening rates,” Wender told AAFP News. “Removal of precancerous polyps resulting from screening undoubtedly accounts for the incidence decline in the older age group, but no guideline recommends screening in average-risk individuals under age 50.”

Wender said it’s important to recognize that CRC in individuals younger than age 50 is still relatively unusual, but certainly not rare.
Study Overview

The retrospective cohort study used the Surveillance, Epidemiology and End Results (SEER) CRC registry to examine patients diagnosed as having colon or rectal cancer from 1975 to 2010. The SEER database represents about 28 percent of the United States population and provides statistical information such as annual cancer incidence rates and annual percentage change (APC). The predicted annual incidence rates were calculated based on the estimated APC by age and cancer site and assumed to change at a constant percentage of the rate of the previous year.

Doug Campos-Outcalt, M.D., M.P.A., of Phoenix, former AAFP liaison to the U.S. Preventive Services Task Force (USPSTF), told AAFP News that the study and its findings raised some concerns for him. First, he said, it is a single study that used observational data from a source that could have potential biases. And second, the results for the younger age groups are presented as relative risk changes rather than absolute risks.

“If the rate is very low to start with, a 100 percent increase may not be too important,” Campos-Outcalt said. “Look at the age group 20-34. The starting rate is 1/100,000 and goes up to about 2/100,000. That is a doubling of the rate but it is still very low. This is the same for the 35-50 (age group)—just somewhat higher but still not common. The rates after age 50 are much higher.”