Colorectal cancer rates are rising in adults under age 50 -- people who are not typically screened for such cancers. The finding, gleaned from a cancer surveillance database and published in the June issue of Cancer Epidemiology Biomarkers & Prevention, reported a 17% increase in this age group over a decade.
Scientists aren't sure why this is happening, but there are some things they know and suspect.
First, some stats: Colorectal cancer (cancer of the colon or rectum) is the third most common cancer in the U.S. in men and women, with nearly 150,000 new cases each year. Close to 50,000 people die of it each year, according to the American Cancer Society.
The good news is that overall, rates of colorectal cancer have been declining in the U.S. for more than a decade -- the result of widespread screening, which either prevents the disease or detects it early enough to treat it successfully.
The risk in younger adults is still low compared with those over 50: Fully 91% of new cases are in people 50 and older. Still, rates have been creeping up in younger people, by as much as 2% per year in certain groups.
The new study found that the rate in white men ages 20 to 49 was 8.4 cases out of every 100,000 people in the period 1992 to 1995. Ten years later (2002-05), the rate had risen to 10.2 -- a 21% increase.
For white women ages 20 to 49, the incidence rate was 6.9 in 1992 to 1995 and 8.8 in 2002 to 2005 -- a 28% increase.
In Latinos, the increases were 33% for men in this age group and not statistically significant for women. There was no increase for African Americans, but the incidence of colorectal cancer in that group is higher than in whites or Latinos: 12.7 and 10.8 cases per 100,000 in 20- to 49-year-old men and women, respectively.
This is not the first report of a rise in colorectal cancer rates among younger groups. A 2004 review of data by UCLA surgeon Dr. Clifford Ko reported a similar increase in U.S. colorectal cancer rates in 20- to 39-year-olds. Ko investigated after a surgical resident said he had recently operated on two patients with colon cancer who were under 40.
Researchers speculate that the increases may be caused, at least in part, by changes in the American lifestyle.
Diets high in red and processed meat have been linked to colorectal cancer, as have diets low in milk and calcium -- a double whammy for a generation raised on burgers and soda at fast-food restaurants. Obesity and low physical activity also are risk factors for these cancers, and obesity rates have risen significantly over the last two decades.
The data for those under 50 could be a harbinger. "We often look at trends in younger adults because they can be an earlier indicator of changes in risk factors and rates overall," says Elizabeth Ward, a senior researcher at the American Cancer Society and an author on the new paper. "As this population ages, their increased risk for colorectal cancer could carry through."
A major factor driving down U.S. colorectal cancer and death rates in the over-50s is wider use of screening, Ward says. Colonoscopy, the mainstay test, detects cancer early. It also can prevent its development by removal of precancerous polyps in the bowel.
But most people under 50 are not screened for colorectal cancers -- only those with certain risk factors, such as family history, chronic inflammatory bowel disease or a predisposing genetic condition. Lack of routine screening gives benign polyps time to turn cancerous and early cancers time to turn invasive.
If the cancer risk increases enough in younger age groups, screening guidelines might be revised to include younger adults, Ko says. "That's not the case yet," he adds. The costs and risks of screening make routine testing of questionable value in a population that is still at low risk.
But Ko says physicians need to be aware of the trend so they don't rule out cancer based on age. "If somebody comes in and they're 39 years old and they have bleeding that isn't due to hemorrhoids, they should get a colonoscopy."
Diet isn't iron-clad protection against colorectal cancer, but it can help reduce risk. The American Cancer Society recommends plenty of fruits, vegetables and whole grains, as well as exercise for at least 30 minutes five days a week.