An American Cancer Society study has found that rates of colorectal cancer (CRC) have risen dramatically in younger adults (younger than 55 years). The increase in incidence is seen particularly among the so-called Generation X (persons born from the early 1960s to the early 1980s) and millenials (persons born from the early 1980s to the early 2000s).
Three in 10 CRC diagnoses now occur among people younger than 55 years, and rates among young and middle-aged adults have returned to what they were for people born around 1890, say the authors.
“People born in 1990 now have double the risk of colon cancer and quadruple the risk of rectal cancer compared to people born around 1950,” first author Rebecca Siegel, MPH, of the American Cancer Society, in Atlanta, Georgia, told Medscape Medical News.
The findings were published online February 28 in the Journal of the National Cancer Institute.
The study, which investigated trends in CRC incidence by year of birth, found that risk for CRC declined until the first half of the 20th century. People born around 1950 have the lowest risk for disease. The risk for CRC began increasing after that date.
To turn the tide, Siegel emphasized that screening should start at age 50 years for average-risk individuals and at age 40 for those with a family history of CRC or adenomas in a first-degree relative.
Lifestyle changes, such as a healthy diet and exercise, are important but will likely take a long time to produce results, she said.
“In the near term, we need educational campaigns to inform the general public about the signs of CRC and to follow up if they have symptoms consistent with the disease. That can move the needle of diagnosis to an earlier stage of disease, where treatment is more effective,” she said.
The increase in CRC rates in younger adults has been highlighted by Medscape Medical News. One study found that 1 in 7 diagnoses of CRC now occur in people younger than 50 years. Another study found that about 14,000 cases of CRC per year occur in people younger than 50, which exceeds the number of cases of acute lymphocytic leukemia, Hodgkin’s lymphoma, and even cervical cancer.
Because screening is not recommended for average-risk individuals younger than 50 years, CRC in younger adults is often “not on anyone’s radar.”
Related to Obesity, Sedentary Lifestyle
Although the latest study did not directly evaluate underlying reasons for the increase in risk, Siegel provided several hypotheses.
But the picture is more complicated than that, because rates of CRC have increased in parallel with the obesity epidemic. If only obesity caused the trend, rates of CRC would be expected to increase 10 or 20 years after the obesity epidemic started, not at the same time. Most likely, other factors related to excess weight, such as a sedentary lifestyle and unhealthy diets, are independently affecting CRC, Siegel explained.
Reasons why rates of CRC are similar for people born in the 1890s and for millennials are anyone’s guess. The combination of risk factors for CRC in the early twentieth century are unknown, but they were likely different from what they are now, she said.
A major concern about the increase in CRC in younger age groups is the risk of being diagnosed with later-stage disease: younger people who have CRC are about 60% more likely to be diagnosed with distant disease than older people, according to Siegel.
“There are delays in diagnosis because younger people aren’t aware of symptoms of cancer. And their primary care doctors aren’t thinking about it in their younger patients,” she said.
Also, younger patients are much more likely to be uninsured, which is associated with diagnosis at a later stage.
“We know that when people have insurance, they have access to care. They’re also more likely to have preventive services, which is very important for diagnosing cancer at an earlier stage,” she said.
The possible repeal of the Affordable Care Act (ACA) is “very concerning,” she added, because of the potential increase in the number of people who are uninsured.
“It’s unknown what will happen. We do know from studies of cervical cancer that young people who have gotten access to care because of the ACA have an earlier stage of diagnosis,” she emphasized.
The possible loss in coverage is especially concerning with respect to CRC, given that the risk for CRC is increasing more rapidly among younger adults. “Repeal of the ACA would mean that these people are pretty out of luck,” she suggested. The US Centers for Disease Control and Prevention does have CRC screening programs for underserved populations, but these programs are a “drop in the bucket,” Siegel said.
Also of concern is that low-cost preventive services that are made available through the ACA may be on the chopping block. That means CRC screening could also decrease among people who have insurance through high-cost plans.
In the current study, researchers evaluated trends in CRC incidence from 1974 to 2013, using the Surveillance, Epidemiology and End Results (SEER) database. The analysis included data from 490,305 adults who were diagnosed with invasive CRC and lived in areas represented by nine of the oldest SEER registries during this period.
Researchers separated the group into birth cohorts and 5-year age groups. They also employed age-period-cohort modeling, designed to parse out factors related to the period (such as changes in medical practice) from factors that differ by generation (such as behavioral changes).
Results showed that in the late 1970s and early 1980s, colon cancer incidence rates were decreasing in people younger than 50 years and were increasing in those older than 50. After the mid-1980s, the trend reversed itself. From the mid-1980s through 2013, colon cancer incidence rates decreased in those aged 55 and older but increased by 2.4% per year in adults aged 20 to 29 and by 1.0% per year in those aged 30 to 39. Beginning in the mid-1990s, rates increased by 1.3% per year in those aged 40 to 49 and by 0.5% per year in those aged 50 to 54.
Rates of rectal cancer have been increasing for a longer time and at faster clip than rates of colon cancer. From 1974 to 2013, rates of rectal cancer increased 3.2% per year in people aged 20 to 29 years. Since 1980, rates increased by 3.2% per year in people aged 30 to 39. Starting in the 1990s, rates increased by 2.3% per year in adults aged 40 to 54.
People aged 55 years and older have experienced generally decreasing rates of colon cancer since the mid-1980s. Rates of rectal cancer have been declining for at least 40 years in this age group.
Around 1990, incidence rates of CRC in people aged 50 to 54 years were about half those in people aged 55 to 59. By 2012-2013, the gap narrowed. Colon cancer rates were only 12.4% lower in those aged 50 to 54 (31.9 vs 36.4; incidence rate ratio [ IRR] = 0.88, 95% confidence interval [CI] = 0.81 – 0.94). Rectal cancer rates were about the same (24.7 vs 24.5 per 100,000 persons; IRR = 1.01; 95% CI = 0.92 – 1.10).
Compared to people born before 1950, those born around 1990 had double the risk for colon cancer (IRR = 2.40; 95% CI = 1.11 – 5.19) and quadruple the risk for rectal cancer (IRR = 4.32; 95% CI = 2.19 – 8.51). Similarly, those born around 1890 had double the risk for colon cancer (IRR = 2.12; 95% CI = 1.91 – 2.36) and triple the risk for rectal cancer (IRR = 3.06, 95% CI = 2.71 – 3.47).
The study was supported by the American Cancer Society and the National Institutes of Health/National Cancer Institute.
J Natl Cancer Inst. Published online February 28, 2017.