The good news: Colon and rectal cancer rates are dropping overall. The bad news: The rates for these cancers are on the rise for younger people. Researchers for a study published in JAMA Surgery pored over a database that included cancer cases from 1975 to 2010 to draw out colorectal cancer rates among different age groups, Reuters reports.

The incidence in all age groups fell 1%, but it rose among those aged 20-49. Scientists aren't sure why younger folks are experiencing these increases, though speculation includes not eating right or exercising, while the incidence of more advanced cancers in younger people may simply be because younger people and their doctors might not suspect colorectal cancer until it's progressed significantly.

If the underlying causes aren't addressed, researchers posit ominous stats: Using a computer model, they predict that by 2030, the number of colon and rectal cancer cases will roughly double among people between 20 and 34 and grow 28% to 46% for people 35 to 49.

As it stands now, there will be an estimated 136,830 new colorectal cases overall by year's end, with about 50,000 deaths, the National Cancer Institute notes.

While an American Cancer Society report indicates more screening may help, a gastroenterology doctor tells Reuters, "We don't want to send the message that people in their 30s should be running out and getting a colonoscopy." An editorial on the new study suggests being mindful of symptoms—bloody stools, unexplained weight loss, bowel movement changes—and eating better.

(A new at-home colon cancer test is now available.)

This article originally appeared on Newser: Colon Cancer Study Brings Good News, Bad News

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