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NEW YORK (Reuters Health) - Rectal cancer rates may be on the rise in people younger than 40, according to a new study that examined more than 30 years of data from a national cancer registry.

The researchers found a steady rate of increasing diagnoses in young people starting around 1984 - an observation they're not sure how to explain. But they caution that the overall risk of rectal cancer is still very low in the under-40 population.

"Although the rate is increasing, it's still a relatively rare phenomenon," Dr. Joshua Meyer, the lead author on the study from Fox Chase Cancer Center in Philadelphia, told Reuters Health. However, he said, "it's something that doctors should be aware of, and I think patients out there should be aware of it as well."

Meyer and his colleagues searched a national cancer registry that covers about one-quarter of the U.S. population for all rectal and colon cancers diagnosed in people less than 40 years old between 1973 and 2005. Cases of rectal and colon cancer are often grouped together, and the two are thought to have similar risk factors.

Over the entire study period, Meyer and his colleagues identified 5,125 people younger than 40 with colon cancer (a rate of about 1 in 90,000 people of that age) and 1,922 with rectal cancer (about 1 in 240,000).

But while colon cancer rates stayed flat over the years, rates of rectal cancer inched upwards, a trend that started around 1984, the authors calculated. Starting that year, the rate of young people diagnosed with rectal cancer increased by almost 4 percent each year until 2005, the authors report in the journal Cancer.

The increasing rates were consistent across races, the authors said, and were found in both men and women separately.

"This is something that is happening on a fairly consistent basis year after year," Meyer said.

Dr. Douglas Rex, who studies colorectal cancer and screening at the Indiana University School of Medicine, said that the increase in rectal cancer would fit with his own anecdotal observations. "When you get a study like this it's always good to make sure that it's reproduced," he said. But, "it looks to me like it's a result that needs to be taken seriously."

Meyer and his colleagues couldn't explain why the trend seems to be occurring. "Essentially all of the risk factors for rectal cancer are the same as those risk factors for colon cancer," Meyer said. "We were really unable to identify anything that could be a suspect for increasing rates of rectal cancer when the colon cancer rates are staying the same."

Those common risk factors include having a family history of the cancer or other hereditary diseases that are thought to be related to colon and rectal cancers, or having a personal history of other types of cancer, including breast and ovarian cancers for women.

People who are diagnosed with rectal cancer before age 40 frequently fare worse than older people with the disease, the authors say - in part because it's often caught later in young people. The overall five-year survival rate for rectal cancer in the United States is between 50 and 60 percent. Cases diagnosed in early stages have better survival rates than those caught later.

Current recommendations suggest that rectal screenings start between ages 45 and 50. Meyer said that the overall rates he and his colleagues identified are still too low to suggest starting screening at a younger age.

However, he said, doctors should consider testing younger patients who come in with some of the most common signs of rectal cancer, such as rectal bleeding, to rule out cancer.

Doctors often chalk these symptoms up to hemorrhoids, Meyer said, but "it seems that there's a good reason to go a little further" and be sure that the patient doesn't have cancer.

Rex agreed. In younger patients, "when blood is going in the toilet bowl...we need to come up with a source for the bleeding and treat it and see it disappear," he said.

SOURCE: http://link.reuters.com/myz95n Cancer, online August 23, 2010.

http://www.reutershealth.com/archive/2010/08/23/eline/links/20100823elin003.html