The study found after decreasing since 1974, colon cancer incidence rates increased by 1% to 2% per year from the mid-1980s in adults aged 20 to 39.
"Trends in young people are a bellwether for the future disease burden", said Siegel in a statement.
We need to delve into this population of young people and see if there is a specific molecular signature to their cancers or if there are any common risk factors, such as obesity or a sedentary lifestyle, which have been suggested.
The data showed a surprising trend: Despite a decrease in colorectal cancer rate for older adults, young adults' rates of colorectal cancers have risen to where they now have the same odds of being diagnosed with colorectal cancer as someone the same age, but born in the 1890s. The American Cancer Society found that now, 3 in 10 rectal cancer diagnoses are in people under the age of 55.
Because routine screening is generally not recommended for most people under 50, these cancers are often found in more advanced stages, too.
But colorectal cancer is increasing in adults between 20 and 39 years old. Currently, screening is recommended to start at age 50.
And whatever is driving the study results may be due to changes in diet, lifestyle or other environmental factors, said Chan, who is also an associate professor in the department of medicine at Harvard Medical School.
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The study published in the Journal of the National Cancer Institute said the number of cases are rising in young and middle aged adults, including people in their early 50s, with rectal cancer rates increasing particularly fast. Overall diagnoses of the disease are going down, but it's mostly younger people who are seeing a change - risks have increased for people between 20 and 54 years old in recent decades.
Researchers note that rates of colorectal cancer have been falling since the 1980s with an even steeper decline in the past decade, which has been caused by more screening.
The study confirms what many doctors have been seeing among their younger patients, said Nilofer Azad, an oncologist at the Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins, who was not involved in the research. The researchers called for expanding screening for the disease earlier in life.
For now, experts say if you experience symptoms of colorectal cancer, you should talk to your doctor. In adults 40 to 54, rates increased by 0.5 to one per cent per a year from the mid-1990s through 2013.
Many young patients have no obvious risks, Weber said, so "we suspect there may be additional factors at play".
They point out in 2013 in the United States, 10,400 new cases of colorectal cancer (CRC) were diagnosed in people in their 40s, with an additional 12,800 cases diagnosed in people in their early 50s.
Rates for adults older than 55 has been declining for about 40 years, researchers said.