SAN FRANCISCO – The incidence of colorectal cancer is rising sharply among younger adults in the United States, a study showed.
Researchers analyzed Surveillance, Epidemiology, and End Results (SEER) data for 383,241 patients in whom colorectal cancer was diagnosed between 1975 and 2010.
The results showed that the age-adjusted incidence rate of colorectal cancer fell steadily among patients aged 50 years and older at diagnosis, lead author Dr. Christina E. Bailey, a surgical oncology fellow at the M.D. Anderson Cancer Center in Houston, reported in a poster session at the annual Gastrointestinal Cancers Symposium. But the rate rose among younger patients.
The annual percentage change in the age-adjusted incidence rate of colorectal cancer during the 35-year period was a significant –0.92 in the cohort overall. In stratified analyses, the annual percentage change fell significantly among patients aged 50-74 at diagnosis (–0.97), and aged 75 years and older at diagnosis (–1.15). But it rose among patients aged 35-49 at diagnosis (0.41) and especially among patients aged 20-34 at diagnosis (1.99).
The findings were similar for colon cancer separately (with strongest results seen for disease that was distant at diagnosis) and for rectal/rectosigmoid cancer separately.
A predictive model suggested that if the observed trends persist between 2010 and 2030, the incidences of colon cancer and of rectal/rectosigmoid cancer will rise by 90% and 124%, respectively, among 20- to 34-year-olds, and by 28% and 46%, respectively, among 35- to 49-year-olds.
Much of the decreasing incidence among older adults "can be attributed to the fact that screening is recommended beginning at the age of 50," Dr. Bailey commented in an interview.
"We saw dramatic rises in the predicted incidences of both colon and rectal cancer in our younger cohort that point out that further studies need to be done to determine why this is happening and what can we do now to prevent this trajectory from occurring in the future," she said at the symposium, sponsored by the American Society of Clinical Oncology.
Likely explanations for this sharp uptick, she suggested, include increasing population levels of obesity and physical inactivity, and consumption of a diet high in fat and red meat – factors implicated as risks for colorectal cancer.
Another possibility is that primary care physicians are now more alert for this cancer in young patients with symptoms such as rectal bleeding, which previously may have been attributed to conditions such as hemorrhoids, delaying diagnosis until an older age.
Recommendations still call for routine colorectal cancer screening only in those patients younger than age 50 who have risk factors such as familial adenomatous polyposis and Lynch syndrome, Dr. Bailey noted. And even though the incidence is rising in the younger age groups, it is still considerably lower than it is among people aged 50 years and older.
Dr. Bailey said she had no relevant financial disclosures.
