Both the incidence and mortality rates of colorectal cancer (CRC) have been decreasing in the United States, a trend that is largely attributed to the widespread screening of persons aged 50 years and older.
However, researchers from the University of Texas MD Anderson Cancer Center in Houston have highlighted a concerning trend: incidence rates are actually rising in young adults.
The most pronounced increase, which was observed in patients between the ages of 20 and 34 years, was in the incidence of colon and rectal cancer at all stages (localized, regional and distant).
The new article was published online November 5 in JAMA Surgery.
The authors analyzed Surveillance, Epidemiology, and End Results (SEER) data for 393,241 patients with CRC between 1975 and 2010 and evaluated the age at diagnosis in 15-year intervals, beginning at age 20.
The overall age-adjusted incidence rates decreased by 0.92% during the study period.
But although there has been a steady drop in incidence among persons aged 50 years and older, the opposite is true for those in younger age groups, according to the authors, led by principal investigator George J. Chang, MD, associate professor, Departments of Surgical Oncology and Health Services Research at MD Anderson.
On the basis of these trends, the authors estimate that by 2020 and 2030, the incidence rate of colon cancer will increase by 37.8% and 90%, respectively, for patients aged 20 to 34 years.
This figure represents a 131.1% incidence rate change of colon cancer by 2030 in younger patients, as compared with patients older than 50 years.
The numbers for rectosigmoid and rectal cancers are similar and are expected to increase by 49.7% and 124.2%, respectively, for this same age subgroup. This extrapolates to a 165% incidence rate change, as compared with older patients.
For those aged 35 to 49 years, the incidence rates are also projected to increase, but at a slower pace: 27.7% for colon cancer and 46% for rectal cancer by 2030.
Doubling of Rates
"We've been seeing a rising incidence rate in younger adults over the past few decades, as the rates in the general population have been declining," said Dr Chang in an interview. "Our current screening programs don't target the younger population. But if these trends continue, we are going to see a doubling in the next 15 years."
One in six cases of colon cancer will occur in patients younger than 50 years, as will one in four cases of rectal cancer, he added.
The authors note that their data are consistent with previous studies that have also used large population-based databases, and they speculate on the possible reasons for this disturbing trend. One is a delay in early detection. Young adults do not undergo routine screening until there is a reason for it, such as a history of familial polyps, and prior to the Affordable Care Act, many patients lacked health insurance, which may have delayed diagnosis.
Younger patients are less likely to be concerned about symptoms and the importance of seeking medical care, Dr Chang pointed out. "Their providers are also less likely to consider cancer as a possible diagnosis."
Behavioral factors, such as obesity and physical inactivity, may also play a role, the investigators note in their study. The prevalence of obesity has risen in the United States, and that is a known contributor to CRC, along with physical inactivity. The typical Western diet is high in red meat, junk food, and processed meats and is low in vegetables; it too has been associated with an increased risk for colon cancer.
No Changes in Screening for Now
But thus far, although this report is "rather unsettling," the author of an accompanying commentary does not believe that it represents a call for changing screening guidelines just yet.
Kiran K. Turaga, MD, MPH, of the Medical College of Wisconsin, in Milwaukee, writes that "assuming that this increasing incidence of colorectal cancer in young adults is a real phenomenon, it begs the question of why this is occurring and what one should do about it."
He points out that although continued epidemiologic investigation into the causality of nonhereditary CRC in this population is crucial, a call for widespread screening by colonoscopy is premature. "It is important to note that the absolute incidence of colorectal cancer in the young adults (aged 20-34 years) is 1% of the total colorectal cancer burden and similarly fairly low in the 35-to-49-year-old age group (6.8%)."
"Hence, widespread application of colonoscopic screening might add risk without social benefit," Dr Turaga adds. "However, this report should stimulate opportunities for development of better risk-prediction tools that might help us identify these individuals early and initiate better screening/prevention strategies."
Strategies Needed
The study authors agree that these results do not call for revisiting screening guidelines at this time. "We tried to highlight that our paper was not designed to address the impact of screening in younger people," said Dr Chang, "And we do need to look at strategies for prevention and early detection. But in terms of absolute numbers, the number of younger patients with CRC is still relatively small."
Younger patients do tend to be diagnosed at a later stage, but whether they typically have disease of a more aggressive course is yet unclear. "We know that all colorectal cancers are not the same, and it could be that young patients may have another subtype," he speculated. "There may be some defining feature, and there is a suggestion that their tumors may be a little different. But I think that the short answer is that we really don't know."
"For now, the key message for patients is to seek care and for providers to consider CRC as part of a differential diagnosis, so a delay can be avoided," Dr Chang said. "And we can all adopt healthier habits, such as exercising and improving our diets. Policy makers should encourage healthier behaviors."
The study was supported in part by grants from the National Institutes of Health and the National Cancer Institute. The authors have reported no relevant financial relationships. Dr Turaga serves as a consultant for Castle Biosciences and Ethicon.
JAMA Surg. Published online November 5, 2014.
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