Colorectal cancer rates have been rising sharply in younger adults even as the rate for the population as a whole has dropped, according to a study published today in the Journal of the National Cancer Institute.
While rates of colon cancer dropped for people 55 and older from the mid-1980's to 2013, the researchers found the risk of a younger adult developing the disease rose 2.4 percent per year in adults in their twenties and by 1 percent per year in adults in their thirties.
By the mid-1990s, rates were also increasing 1.3 percent per year in adults in their forties and 0.5 percent for adults between the ages of 50 and 54.
Dr. Jordan Berlin, co-leader of the Gastrointestinal Cancer Research Program at Vanderbilt University Medical Center, said the upwards trend among young people has been seen in recent studies but that the new study was still surprising.
"It's an interesting study because the rise in the youth comes with a fall in other ages," said Berlin, who was not involved in the study.
For rectal cancer, the increase was even more striking. Incidence of rectal cancer in people in their twenties rose by 3.2 percent per year from 1974 to 2013. From 1980 to 2013, the incidence of rectal cancer for people in their thirties also increased 3.2 percent per year. For people in their forties and fifties, the rates of rectal cancer increased 2.3 percent starting in 1996, the study found.
Researchers from the American Cancer Society and the National Cancer Institute looked at colorectal cancer rates from 1974 to 2013 using data from the National Cancer Institute's Surveillance, Epidemiology and End Results Program. They found 490,305 patients over the age of 20 were diagnosed with colorectal cancers from 1974 to 2013.
Despite these upticks among people under the age of 55, overall the rates of colorectal cancers have been dropping for decades, with the pace accelerating to a 3 percent drop annually from 2003 to 2012, the study found. The lifetime risk of developing colorectal cancers remains small at approximately 4.4 percent, according to the National Cancer Institute.
With a third of rectal cancer patients under the age of 55, the study authors question if the medical community should consider screening before age 50.
Researchers did not specifically study possible reasons why the colorectal cancer rate has increased so dramatically in younger adults.
Understanding this increase in cancer rate will take much more research, Berlin said. While increased screening for those over 50 may mean catching potential pre-cancerous polyps before they become cancerous, Berlin said much more study will need to be done to understand why there has been such a significant increase.
"One would have to think that lifestyle may play a role," Berlin said, positing that a more sedentary lifestyle and obesity increase risk of cancer.
In addition, understanding how our current diet -- often high in saturates fats, sugars and grains -- can affect cancer risk may be key in understanding the rise in colorectal cancer rates among younger adults, Berlin said.
"Our diet, which would be considered a Western diet, has a higher risk for colon cancer," Berlin said. "We have certainly changed our diet from the 1950's to 1990's."
However, the increase in colorectal cancer risks should not make younger people feel overly fearful, Berlin said, noting that there are key symptoms that could signal something is wrong and lead a person to talk to their doctor.
One tip-off is "if your bowel habits change and stay consistently changed," Berlin said.
Additionally, blood in the stool, abdominal pain, narrowing of the stools, and for men, developing anemia, are also all possible indicators of colorectal cancer, he said.
The new study adds to a growing body of evidence about the risk of colorectal cancer among younger adults, which could impact current screening guidelines, Berlin said.
Current guidelines advise people without other risk factors to start colonoscopies every 10 years at age 50. The risk of a young person developing colorectal cancer remains overall very low. A 50-year-old man is nearly 10 times as likely to develop colorectal cancer over a decade compared to a 30 year man, according to the U.S. Centers for Disease Control and Prevention.
"The most important question is do we need to screen sooner," Berlin said.