The last

Rates of colorectal cancer are rising rapidly among adults in their 20s, 30s and 40s, and the most common warning sign of the disease is passing blood in the stool, according to a new scientific review.

Rectal bleeding is associated with a five-fold increased risk of colorectal cancer, according to the new analysis, which looked at 81 studies involving nearly 25 million adults under age 50 worldwide.

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 Thursday in the journal JAMA Network Open.

Because it is important

Rates of colon and rectal cancer have increased among younger adults as rates have decreased among older people, who are much more likely to have colonoscopies that can detect cancers and precancerous lesions called polyps.

But although millennials born around 1990 have almost twice the risk of colon cancer compared to people born in the 1950s, and have a four times greater risk of rectal cancer, young people without a strong family history of cancer colon ineligible for colonoscopies until age 45.

Doctors may also miss warning signs. Anecdotal evidence suggests that because doctors are less likely to suspect malignant diseases in younger people, they may attribute a symptom like rectal bleeding to a benign condition like hemorrhoids, rather than cancer, said Joshua Demb, an oncologic epidemiologist. from the University of California, San Diego. and one of the main authors of the article.

From the time younger adults first go to a caregiver with a complaint about a symptom to receiving a diagnosis, it can take four to six months on average, the analysis found. Because diagnosis is often delayed, younger adults tend to have more advanced and harder-to-treat disease.

“We need to make early detection easier, and one way is to identify 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, sedentary lifestyle, high alcohol consumption, and diets high in red meat, processed foods, and sugary drinks.

New research exploring the rapid rise of 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.