Colon cancer is often thought to affect older people, but one in five cases diagnosed today occurs in people younger than age 55, compared with one in 10 cases in 1995, according to a recent study published by the American Cancer Society.
There is no clear explanation for this trend, but a new paper has just been published Science suggests a number of possible reasons, including environmental and genetic factors. Low screening rates and misdiagnoses in people who don’t suspect cancer are also likely to play a role.
“We’re getting to a point where we shouldn’t think of colorectal cancer as a disease of older adults only,” said Andrew Chan, a professor of medicine at Harvard Medical School and vice chairman of gastroenterology at Massachusetts General Hospital.
The findings also revealed an increase in advanced disease diagnoses, which is particularly concerning because colonoscopies “are a great tool for prevention and early detection of colorectal cancer in terms of screening that can actually detect and remove precancerous lesions,” said lead author Rebecca Siegel. senior scientific director of cancer surveillance research at the American Cancer Society. Survival rates are 90 percent if detected early enough.
Rising rates in younger adults led the U.S. Preventive Services Task Force to change its recommendation in May 2021 to start screenings at age 45 instead of 50, but those with risk factors may need to start even earlier, said Siegel, who noted that nearly a third of colorectal cancers are associated with a family history of the disease.
“Until we see these trends start to reverse, we’ll have to keep thinking about what appropriate strategies to take to really halt this rise in early disease,” Chan said.
Identifying colorectal risk factors
Genetic risk scores could be useful to identify those more likely to develop colorectal cancer at a young age, but could be more effective if they account for interaction with environmental factors, suggested Marios Giannakis, an oncologist at the Dana-Farber Cancer Institute who co-authored the Science paper. The question is which environmental factors? Finding that out requires long-term studies of large populations that are expensive and difficult to conduct, especially since they would be most useful if they included stool, blood, and tissue samples collected over time.
Lifestyle factors may initially seem like an easy culprit for early illness, but the reality is more complicated. Being overweight increases the risk of colorectal cancer, Siegel said, but only about 5 percent of colorectal cancers are attributed to being overweight. Being overweight is also associated primarily with tumors on the right side of the colon, not the left colon, which is where the Cancer Society found the increase takes place.
Being overweight is also a greater risk factor for men than for women, but the trend in younger adults is similar for all people.
“Diet, obesity and physical inactivity may account for some of this increase, but it’s not the full story,” Chan said. “There are other contributors that have yet to be discovered, and I think it’s those factors that we really need to focus our attention on, because they’re going to be things that can potentially have a bigger impact on reducing incidence.”
Giannakis’ article notes that higher consumption of sugar-sweetened beverages, as well as reds and processed meats, are possible factors. Others include “antibiotics, more ubiquitous environmental toxins, and higher rates of cesarean sections and other surgical procedures.”
What all of those factors have in common is an effect on the microbiome, the population of bacteria and other microorganisms that populate the human digestive system. Mark A. Lewis, director of gastrointestinal oncology at Intermountain Health in Utah, said in a 2019 study from the United Kingdom that the early onset of the disease is at least “partly explained by antibiotic use in childhood and young adulthood, as has been most convincingly shown”.
Don’t ignore troublesome symptoms
It’s challenging to figure out how much increased mortality is due to greater risk factors versus low screening rates, especially in rural or low-income areas, but it’s probably both, said Rishi Naik, an assistant professor of medicine in gastroenterology. enterology, hepatology and nutrition at Vanderbilt University Medical Center.
Screening gaps are evident in the fact that 27 percent of younger adults are diagnosed with advanced disease, compared to 20 percent of older adults. Survival rates are similar between ages, despite younger patients typically receiving more aggressive treatment and having fewer other conditions.
“We fear this may also indicate a more aggressive biology for reasons we need to understand,” Giannakis said, but it’s still not clear whether disease in younger people is more aggressive or just caught too late or both. Siegel’s paper noted that symptomatic patients under age 50 took 40 percent longer to receive a diagnosis compared to older patients.
“It is important for patients and caregivers to aggressively investigate symptoms and signs, such as rectal bleeding and unexplained iron deficiency, to ensure that unsuspected colorectal cancer is not the cause, regardless of age,” said Reid Ness, associate professor of medicine. in gastroenterology, hepatology and nutrition at Vanderbilt University Medical Center.
The most common symptoms of colon cancer in younger patients are abdominal pain; unexplained weight loss; changes in the frequency, size, or appearance of stools; and rectal bleeding, which occurs in 46 percent of early-onset cases compared to 26 percent of cases in adults over age 50.
“Young people tend to assume they’re young and healthy, and if they have symptoms, that it’s something transient or nothing to worry about,” Chan said. Siegel also pointed out the importance of fighting stigma, as people may not feel comfortable discussing rectal symptoms. But following up means making sure doctors take the symptoms seriously, too.
“Sometimes the more unfortunate stories are patients being told they just have a hemorrhoid, and a few months later they have metastatic colon cancer,” Naik said. “If they’re symptomatic, they need a colonoscopy and not just a stool-based test.”
Health disparities show that there is a need for more screening
Like the trend toward more cases at a younger age, racial and ethnic disparities in colorectal cancer rates and deaths are likely due to a combination of greater risk factors and lower rates of screening and access to health care.
Siegel emphasized that Alaskan Natives have the highest rates of colon cancer in the world. The number of cases in this population is more than double that of white individuals, and the number of deaths is nearly four times higher in the Alaskan Indigenous population – the only racial or ethnic group in which the total number of cases is not decreasing. In fact, cases are increasing at a rate of 2 percent each year and remain the most commonly diagnosed cancer in this group.
Possible contributing risk factors for cases in this population include vitamin D deficiency due to less sun exposure, smoking, obesity and a diet high in smoked fish and low in fiber, fruits and vegetables, according to Siegel’s study.
The disparity between cases and deaths is more striking among black Americans, whose case rate is 21 percent higher than white Americans, but whose death rate is 44 percent higher. Three-year survival rates for metastatic rectal cancer are 30 percent for patients diagnosed between 2016 and 2018 — up from 25 percent a decade earlier — but three-year survival rates for black patients have risen to 22 percent, likely due to less access to improved treatments, write Siegel and her co-authors.
Geographical disparities are similarly caused, at least in part, by increased smoking and obesity, as well as lower income and poorer access to health care, Siegel said. Both the number of cases and the death rate are lowest in the west and highest in the Appalachian Mountains and parts of the South and Midwest.
“If you look at a map of county-level poverty and colorectal cancer mortality at the county level, they’re remarkably similar,” Siegel said. Obesity and poorer diets are more common among lower-income families, mainly because processed foods are cheaper and less likely to spoil than fresh foods, Siegel said.
Another factor contributing to disparities is insufficient information about screening options besides colonoscopy, Naik said. Colonoscopies require visits to centers, which are scarcer in Alaska and rural areas. Colonoscopies also usually include anesthesia, which means the patient must take time off from work and bring someone else home, who may also need time off — all of which is more difficult for low-income earners.
“While colonoscopies are a gold standard for colon cancer screening, it’s not the only modality,” Naik said. “We also have stool tests, which you can do at home.” While health care providers play a critical role in driving screening, “health systems really need to step up their efforts to engage communities at the programmatic level,” he said.
Ness takes that idea even further. “The greatest source of disparity in colorectal cancer incidence and mortality remains low screening rates among the uninsured and low-income people,” he said. “Until we commit to the concept and practice of universally available primary health care, including colorectal cancer screening, in the United States, we will continue to see disparities in health outcomes.”