(Reuters)

Colon cancer, like many other cancers, was thought to be a disease of the old.

The nation's leading physician groups don't even recommend screening for colon cancer if you are at average risk unless you are 50 or above. But a new study, published in JAMA Surgery Thursday, challenges those assumptions and raises questions about whether our current standards for screening and care are adequate.

In a retrospective study looking at  393,241 patients from 1975 to 2010, researchers from the University of Texas MD Anderson Cancer Center found that while the overall incidence of colon and rectal cancer has decreased since 1998, there has been an increase in the young. That includes both the 20 to 34 age group and the 35 to 49 year olds. If this rate of increase continues, the study predicted, the incidence rates will be about double for those 20 to 34 years and will increase by 28 percent and 46 percent for those who are 35 to 49 year olds.

The authors, led by Christina Bailey from the department of surgical oncology at MD Anderson, said they couldn't explain the spike in colon and rectal cancers in the young but that the decrease in older adults is likely due to better screening and treatment options. "Further studies are needed to determine the cause for these trends and identify potential preventive and early detection strategies," they wrote.

Colon cancer is among the most deadly cancers, with a significant number dying within five years of diagnosis. According to the National Cancer Institute, nearly 97,000 people will be newly diagnosed with colon cancer and 40,000 with new rectal cancer this year and about 50,000 people will die from those cancers.

Doctors recommend that those at risk due to a family history of the disease or have a certain genetic mutation that may make them more likely to get colon or rectal cancer get regular screenings. The American Cancer Society also recommends diet changes -- eating five or more fruit or vegetables servings a day -- and limiting alcohol intake. Scientists are working on possible vaccines for colon cancer but they are still in the early stages of development.

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