Colorectal cancer remains rare in children and young adults, but diagnoses are rising among children, teenagers and very young adults in the United States. New research suggests that cases diagnosed in people in their early 20s and younger may also be more aggressive than those typically seen in older adults, although the reasons for both trends remain uncertain.
Colorectal cancer affects the colon and rectum and is primarily associated with aging. According to a 2026 study published in the journal Colorectal Cancer, 55% of cases occur in people aged 65 and older, while just 16% occur in people aged 49 and younger, according to the American Cancer Society’s flagship magazine. Only a few hundred cases are diagnosed each year in people younger than 21 in the United States.
Even so, incidence among the youngest age groups is increasing while rates among older people are declining or remaining stable. Regular colonoscopies for people over 50, which can detect and remove precancerous polyps, are likely a major reason for the decline among older adults. Researchers suspect that environmental and lifestyle factors, including ultra-processed foods and sedentary behavior, could be contributing to the increase among younger people.
The gut microbiome may offer clues
Researchers are investigating whether changes in the gut microbiome — the community of bacteria and other microorganisms living in the digestive tract — could help explain the trend.
“Most of the research has actually focused on the gut microbiome, which is the community of bacteria and other microorganisms that live in the gut,” said Dr. Christopher Liu, a professor of medical oncology at the University of Colorado Anschutz and a medical adviser to the Colorectal Cancer Alliance.
Disrupting the microbiome may promote inflammation, which can contribute to cancer-causing DNA mutations. However, Liu said the mechanisms are complex and there is probably no single explanation for why the microbiomes of young people may be changing.
“It’s going to be a lot more complicated than that,” he said.
Colorectal cancer appears more aggressive in younger patients
Researchers are beginning to find that colorectal cancer in people in their early 20s and younger tends to be more aggressive than the disease commonly seen in older adults.
“We feel like this is a slightly different disease than what we see in older adults,” said Dr. Erica Arnold, a pediatric surgery fellow at Nationwide Children’s Hospital in Columbus, Ohio. Arnold presented new research on colorectal cancer in people under 21 at the annual meeting of the American Academy of Pediatrics in October. The research is available through the meeting’s poster information.
Arnold and her colleagues analyzed 84 patients diagnosed between 2012 and 2023. The median age at diagnosis was 16, and the median duration of symptoms before diagnosis was 12 weeks.
Only about 20% of the patients had a close family member with colorectal cancer, suggesting that many of the young patients did not develop the disease because of an obvious inherited risk factor.
“If you want my honest opinion, I would suggest that these cancers progress differently.”
Dr. Christopher Liu, professor of medical oncology at the University of Colorado Anschutz
About 80% of the study participants were diagnosed with stage III or stage IV cancer. At those stages, the disease has spread locally to lymph nodes or to more distant organs. By comparison, 60% of colorectal cancer patients of all ages are diagnosed at stage III or IV, according to the Centers for Disease Control and Prevention.
Arnold also said that one-third of the patients had cell markers associated with particularly aggressive cancers.
“Some of that may be related to delayed diagnosis. But if you want my honest opinion, my suggestion is that these cancers progress differently,” Liu said.
Young people are being diagnosed more often
Although Arnold’s study was not nationally representative, a recent analysis of CDC data also found that colorectal cancer incidence is increasing among young people.
Between 1999 and 2020, the diagnosis rate for children aged 10 to 14 rose from 1 in 1 million to 6 in 1 million. Among teenagers aged 15 to 19, the rate increased from 3 in 1 million to 13 in 1 million.
The cause remains unknown
There is no definitive explanation for the increase, Liu said. Research into the microbiome has examined possible links with processed foods, while studies of childhood antibiotic exposure have considered how antibiotics may affect the gut. Stress, lower levels of physical activity and other lifestyle factors could also contribute to colorectal cancer risk.
Some microorganisms may be especially important in colorectal cancer. Certain variants of the common gut bacterium Escherichia coli are strongly associated with colorectal cancer. These bacteria can carry a gene segment that produces a compound capable of damaging DNA. However, this mutation alone cannot explain all cases of colorectal cancer in young people, and it is not clear why changes in the gut microbiome occur in the first place.
“It could be a combination of food, antibiotic use and environmental exposure,” Liu suggested.
Symptoms can be easy to overlook
Arnold’s study also highlighted the importance of investigating persistent symptoms in young people. Among the 84 patients, 75% reported back or abdominal pain before diagnosis, 45% experienced changes in bowel movements, 43% had unexplained weight loss and 38% reported rectal bleeding.
These are common symptoms of colorectal cancer, but they can also have more routine causes and may be overlooked in younger patients, Arnold said.
Liu emphasized that most cases of abdominal pain or gastrointestinal problems in children are not caused by colorectal cancer, which he described as a “very rare event.” However, persistent or worsening pain and gastrointestinal discomfort should be evaluated. Symptoms such as unexplained weight loss and blood in the stool are particularly uncommon in children and require attention.
“It’s important to investigate that to make sure we can catch colorectal cancer in these patients earlier rather than later,” Arnold said.
This article is for informational purposes only and does not provide medical advice.
Source: www.livescience.com