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.
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."
Minimizing This Trend
No matter the level of severity, CRC is increasing among younger adults, said Wender, and the reason for the rising incidence is unknown.
"Although rising obesity rates or other changes in diet are a proposed explanation, the link is far from certain, particularly for cancers in the very young," he said. "Searching for the causal factors for this increase defines a high-priority research question."
In addition to calling for more research to understand the cause of the rising incidence, Wender said there are important steps family physicians can take to minimize morbidity and mortality associated with this trend.
"Young people get colon cancer," he said. "All rectal bleeding must be explored, and a definitive diagnosis must be established. Rectal bleeding should not be attributed to hemorrhoids without proof. New gastrointestinal symptoms, including pain, bloating and change in bowel habits, must also be investigated in young people, just as we do for people older than age 50."
Wender added that family histories are critically important. Guidelines indicate that anyone with a first-degree relative who has had CRC or polyps is at increased risk, he said.
What Happens Next?
As more research explores the seriousness of this trend and its possible causation, Campos-Outcalt suggested family physicians use this opportunity to present the findings as reinforcement to suggest appropriate patients receive the HPV vaccine, because some of the rectal cancers may be HPV-related.
As for whether a USPSTF recommendation on CRC(www.uspreventiveservicestaskforce.org) currently being updated for 2015 might possibly be amended to include screening young adults, Campos-Outcalt said the task force will look at all of the available data and not just a single observational study when assessing upcoming recommendations.
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