Colorectal cancer rates in younger people have surged in recent years. More troubling, most cases diagnosed are at an advanced stage and researchers aren’t sure what’s causing the cancers.
According to new statistics from the American Cancer Society, the proportion of colorectal cancer that occurred in people under age 55 doubled between 1995 and 2019, from 11% to 20%.
That means that, of the roughly 1.3 million people in the U.S. living with colorectal cancer in the United States in 2019, about 273,800 were younger than age 55.
People born after 1990 — millennials and Gen Zers — are twice as likely to be diagnosed with colon cancer and fourfold more likely to get rectal cancer compared to people born in 1950, a 2017 study published in the Journal of the National Cancer Institute found.
The numbers are climbing at an alarming rate. A study published in 2021, in JAMA, estimated that in just seven years, colorectal cancer will be the leading cause of cancer deaths in people ages 20–49.
“This is in stark contrast to people over the age of 50, who are eligible for screening, where rates and deaths from colorectal cancer have been steadily declining for many decades,” Dr. Kimmie Ng, director of the Young-Onset Colorectal Cancer Center at the Dana Farber Cancer Institute, said in an interview.
The new statistics also showed advanced-stage diagnoses are climbing quickly in all colorectal cases in the U.S., jumping from 52% in the mid-2000s to 60% in 2019.
Most cases diagnosed in younger people are advanced stage cancers, said Ng. Advanced or stage 4 cancer is often cancer that can't be cured or doesn't go away completely with treatment, but can sometimes be controlled.
“This cancer type is particularly asymptomatic and can remain that way for a long time," said Dr. Folasade P. May, an associate professor of medicine in the University of California, Los Angeles Vatche and Tamar Manoukian Division of Digestive Diseases. "So the tumor can grow and grow and even spread before there are symptoms that prompt someone to seek medical attention.”
Many younger adults are still not aware that colorectal cancer can happen to them, which may lead them to pass off early symptoms as something else, May said.
Misdiagnoses have been found to be common among young people with colon cancer, previous research suggests.
“When I was training in medicine I was taught this was an old person’s disease, specifically an old man’s disease,” May said. “We know it’s now affecting people in the prime of their lives.”
Why is colon cancer increasing in younger people?
Known lifestyle risk factors including higher rates of obesity, younger people living more sedentary lifestyles than they used to, and eating diets rich in sugars and processed foods all likely contribute to the uptick.
“It isn’t just diet and lifestyle, there is something else,” Ng said in an interview. “We see so many young patients with colorectal cancer who follow very healthy lifestyles and diets.”
The new data show the highest rates of colorectal cancer diagnoses are being diagnosed in:
- Alaska Natives (88.5 per 100,000)
- Native Americans (46.0 per 100,000)
- Black Americans (41.7 per 100,000).
From 2010 through 2019, the incidence rate of colorectal cancer rose in every racial and ethnic group in the U.S.
Genetics, including a family history of Lynch syndrome or polyps, do play a role in a person’s colorectal cancer risk, but only account for about 25% of cases in young people, according to Phillip Daschner, the program director of the cancer immunology, hematology, and etiology Branch of the National Cancer Institute’s Division of Cancer Biology.
“The other 75% of these cases fall into this category of unknown cause,” he said.
The driver is most certainly a combination of environmental factors, May said.
“When something is affecting people who have their birth years in common, then we know it’s something in the environment that has led this whole group of people to have higher rates,” she said.
The phenomenon is called the birth cohort effect.
It’s still not clear what environmental factors beyond lifestyle and diet are at play, but researchers are looking at everything from antibiotics to plastics to stress as potential culprits. It’s also possible there is an environmental toxin that hasn’t yet been linked to colorectal cancer.
“The bottom line is we don’t know why this is happening,” Daschner said.
When should I screen for colon cancer?
Colorectal cancer is still rare among people younger than 50, but the recommended age a person should begin screening was lowered in 2021 from 50 to 45.
Since the adjustment happened in the last couple of years, the increase in cases among people younger than 55 cannot be attributed to increased screening, Ng said. The fact that more cases are being found in advanced stages also rules out increased screening as the reason diagnoses are increasing.
“If it were just a screening effect, we would expect more localized cases to be diagnosed. But that is unfortunately not what we are seeing,” Ng said.
About 40% of young onset colorectal cancers are diagnosed in people ages 45–49. The lowered screening age will be able to catch cancers in this group of people. However, the cases increasingly being diagnosed in people in their 20s or 30s will still likely go unnoticed until symptoms develop.
“Research into what the underlying causes are and what the risk factors are, is so important. We need to identify those young people who are at high risk and target them for earlier screening,” Ng said.
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Symptoms of colon cancer
The most common symptoms of colorectal cancer include:
- blood in the stool
- abdominal pain
- unintentional weight loss
- a change in bowel habits.
- Anemia, shortness of breath and fatigue could also be warning signs.
Part of the problem for doctors and patients is that symptoms can resemble other conditions, experts say. If any of the symptoms appear and do not get better — especially if someone experiences more than one symptom — it should be considered a warning sign.
Research suggests that if caught early while the colon cancer is still localized, the five-year survival rate is around 90%.