One in seven colon and rectal cancers in the U.S. are now diagnosed in patients younger than age 50, which is when people are advised to begin routine screenings for these tumors, a new study finds.

By 2030, nearly one in four rectal tumors and more than one in 10 colon cancers will be diagnosed in people under 50, researchers estimate in the journal Cancer.

"Colorectal cancer has traditionally been thought of as a disease of the elderly; this study is really a wake-up call to the medical community that a relatively large number of colorectal cancers are occurring in young people," said senior study author Dr. Samantha Hendren of the University of Michigan in Ann Arbor.

Researchers analyzed cancer registry data from 1998 to 2011 for about 258,000 patients with colorectal tumors and found that 37,847 of them, or almost 15 percent, were diagnosed before age 50.

Compared with older patients, those under 50 were 30 percent more likely to be diagnosed with tumors that had spread to the lymph nodes and 50 percent more likely to have cancer that had advanced to other organs, the study found.

Younger patients with tumors that had metastasized, or reached other organs, were also more likely than older people to get more aggressive treatments.

About 72 percent of people under 50 got surgery, compared with 63 percent of older individuals. And while 53 percent of younger patients received radiation, just 48 percent of older people did.

Even though patients diagnosed younger tended to have more aggressive disease, they also lived slightly longer without tumors returning after their initial course of treatment.

Five-year survival odds were about 95 percent for patients under 50 diagnosed with local tumors that hadn't spread yet, compared to roughly 92 percent for older people.

With tumors that spread to the lymph nodes, five-year survival rates were 76 percent for young people and 70 percent for older patients, while with cancers that metastasized to other organs the survival odds were 21 percent versus 14 percent, respectively.

One shortcoming of the study is that researchers lacked data on family history and other risk factors for colorectal cancers, the authors note. It's also possible that treatment choices and overall survival were influenced by what's known as selection bias, when healthier people may get more interventions and have better outcomes.

Often, patients may get an early warning of colorectal tumors with symptoms such as bleeding, changes in bowel habits or pain when going to the bathroom that can point to the need for diagnostic screening, said Dr. Joel Randolph Hecht, director of the gastrointestinal oncology program at the David Geffen School of Medicine at the University of California Los Angeles.

"Unfortunately, these symptoms are often ignored by the patient or doctor or ascribed to something like hemorrhoids," Hecht, who wasn't involved in the study, said by email.

There are guidelines for screening some people starting at age 40 if they have a family history of colorectal cancer, noted Dr. Sidney Winawer of Memorial Sloan Kettering Cancer Center in New York.

"Without a family history, physicians need to use their judgment when seeing young people who have bowel symptoms and refer those of concern to a gastroenterologist for a diagnostic workup, " Winawer, who wasn't involved in the study, added by email. "This is difficult since we do not wish to expose young people to unnecessary tests."

It isn't clear from the study findings, however, whether changing preventive screening guidelines to start at a younger age would ultimately prevent more cancer deaths, said Dr. David Weinberg, chairman of medicine at the Fox Chase Cancer Center in Philadelphia.

"If the goal of screening is disease prevention, as it generally is for colorectal cancer, it is not clear when screening should start," Weinberg, who wasn't involved in the study, said by email. "Too early and the yield of screening will be very low since young people are still less likely to get colorectal cancer than older people."

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