MONDAY, June 8, 2009 (HealthDay News) -- Despite a steady decline in colorectal cancer rates in the United States in the past two decades, new research indicates that the disease is actually on the upswing among people younger than 50.
The analysis suggests that the well-established drop in new diagnoses -- now running annually at 2.8 percent and 2.2 percent among American men and women, respectively -- is mainly confined to people older than 50. That is the age at which various forms of routine disease screening -- such as a colonoscopy -- are initially recommended to identify and remove problematic polyps.
"In recent years, we've been thinking we've been doing pretty well because colorectal cancer incidence has been declining overall," said the study's lead author Rebecca L. Siegel, a manager of surveillance information in the department of surveillance and health policy research at the American Cancer Society. "But we found that when you look at young adults, the rates are increasing fairly rapidly -- in great contrast to what's going on in the older population."
To get a handle on the trends, Siegel and her team reviewed data on about 11,000 men and 9,800 women younger than 50 that was gleaned from 13 U.S. cancer registries that tracked information from 1992 through 2005.
During this time, the researchers found, colorectal cancer rates increased 1.5 percent a year among men younger than 50 and 1.6 percent a year among women younger than 50.
Specifically, among non-Hispanic white adults, the research team noted that much of the increase was attributable to a rise in rectal cancer rates. During the study period, rectal cancer increased by an average of 3.5 percent a year among men and 2.9 percent a year among women, the study found.
The researchers also found that incident rate increases for colorectal cancer had edged up in every age category below 50 -- namely, among those 20 to 29, 30 to 39 and 40 to 49.
But the largest bump occurred in the youngest age group, those between 20 and 29 years old. Incident rates in this age range rose 5.2 percent a year in men and 5.6 percent a year in women.
Siegel said more research is needed to identify the underlying cause for the age disparity in colorectal cancer rates.
"We aren't sure exactly what's going on," she said. "But, clearly, I think the increased rates among younger adults, while low, are substantial and need some attention. For now we can say that there is obviously an obesity epidemic going on in the U.S., and so that probably has something to do with it. Also, there has been a change in dietary patterns over the past couple of decades, reflected in an increase in fast-food consumption and red meat consumption among young people."
"But whatever the cause, I would say clinicians should perhaps be more aware of the risks involved when younger people in their 20s and 30s come in with symptoms for what could be colorectal cancer," Siegel added. "This current finding suggests that perhaps clinicians need to act on the risk a little bit more aggressively."
The findings are in the June issue of Cancer Epidemiology Biomarkers and Prevention.
According to American Cancer Society estimates, 106,000 new diagnoses of colon cancer are projected in the United States this year, along with almost 41,000 new cases of rectal cancer. The numbers will include about 15,000 people younger than 50, Siegel noted.
An estimated 50,000 people will die from the diseases combined this year.
Dr. Warren Enker, a colorectal surgeon and vice chairman of surgery at Beth Israel Medical Center in New York City, said that the new analysis "doesn't surprise me in the least."
"A dietary cause makes sense," he said. "If you take kids who are in an environment where the general caloric intake is higher, a sedentary lifestyle is more prevalent than it was 30 years ago and the type of food they're eating -- as regards red meat -- is higher, and then you put all of those things together, then there is no surprise that you have a rising incidence of colon cancer among younger people relative to others."
But Enker, who is also director of the G.I. Institute for Continuum Cancer Centers of New York, cautioned that more research is needed on other factors, such as smoking history and socioeconomic background, that might influence colorectal cancer rates.
The American Cancer Society has more on colorectal cancer.