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Colorectal cancer rates are rapidly rising among adults in their 20s, 30s and 40s, and the most common warning sign for the disease is passing blood in the stool, according to a new scientific review.
Rectal bleeding is associated with a fivefold increased risk of colorectal cancer, according to the new analysis, which looked at 81 studies that included nearly 25 million adults under 50 from around the world.
Abdominal pain, changes in bowel habits and anemia are other common warning signs of the disease and should not be ignored, said the researchers, who published the paper on Thursday in the journal JAMA Network Open.
Why It Matters
Colon and rectal cancer rates have risen among younger adults as rates have declined among older people, who are far more likely to get colonoscopies that can catch cancers and precancerous lesions called polyps.
But though millennials born around 1990 are at almost twice the risk of colon cancer compared with people born in the 1950s, and have a risk of rectal cancer that is four times as high, young people without a strong family history of colon cancer aren’t eligible for colonoscopies until the age of 45.
Doctors may also miss the warning signs. Anecdotal evidence suggests that because physicians are less likely to suspect malignancies in younger people, they may attribute a symptom like rectal bleeding to a benign condition like hemorrhoids, rather than cancer, said Joshua Demb, a cancer epidemiologist at the University of California, San Diego, and one of the paper’s lead authors.
From the time younger adults first go to a caregiver with a complaint about a symptom until they receive a diagnosis can take four to six months on average, the analysis found. Because the diagnosis is often delayed, younger adults tend to have more advanced disease that is harder to treat.
“We need to facilitate early detection, and one way is identifying these red flags,” Dr. Demb said.
What We Don’t Know
The causal factors driving the rise in colon and rectal cancers in younger adults were not addressed in the new analysis, and are not well understood.
Colorectal cancer has long been associated with obesity, smoking, a sedentary lifestyle, high alcohol intake and diets that are rich in red meat, processed food and sugary drinks.
New research exploring the rapid rise in colorectal cancer in younger adults is examining other possible causes, including environmental exposures, changes in gut bacteria and the use of some medications, such as antibiotics.
