Adults born in 1990 are twice as likely to be diagnosed with colon cancer and four times as likely to be diagnosed with rectal cancer as people born in 1950, according to a retrospective analysis published in Journal of the National Cancer Institute.
Further, three in 10 rectal cancer diagnoses are now made in patients aged younger than 55 years.
Rebecca L. Siegel
“Causes for the rise in colorectal cancer (CRC) are unknown,” Rebecca L. Siegel, MPH, director of surveillance information in the Surveillance and Health Services Research Program at the American Cancer Society, told HemOnc Today. “Our finding that CRC risk for millennials has escalated back to the level of those born in the late 1800s is very sobering.
“We hypothesize that some of the factors known to increase CRC risk, including excess body weight; sedentary behavior; high consumption of red/processed meat; and low consumption of fruits, vegetables, and dairy products (calcium) have probably contributed to the increase,” Siegel added. “Notably, the rise in CRC parallels the obesity epidemic, which implicates those behaviors thought to have driven the high obesity rates, like being less physically active and eating less healthy.”
Overall, CRC incidence rates have been declining in the United States since the mid-1980s, with steeper drops in the past decade driven by increased screening. However, recent studies have reported increased CRC incidence in adults aged younger than 50 years, for whom screening is not recommended.
Still, these studies have not examined the temporal trend simultaneously by age, calendar period and year of birth.
To characterize trends in population-based CRC occurrence by tumor location, age at diagnosis, and year of birth, researchers used age-period-cohort modeling, a quantitative tool designed to disentangle factors that influence all ages — such as changes in medical practice — from factors that vary by generation, typically due to behavioral changes.
Siegel and colleagues evaluated data from 490,305 patients aged 20 years and older diagnosed with invasive CRC from 1974 through 2013 and registered in the nine oldest SEER program areas (Atlanta, Connecticut, Detroit Hawaii, Iowa, New Mexico, Seattle-Puget Sound, San Francisco-Oakland and Utah).
Researchers calculated incidence rate ratios (IRRs) for 11 age groups, beginning with 10-year increments (20-29 years, 30-39 years and 40-49 years) and continuing in 5-year increments through age 85 and older.
CRC incidence rates decreased from the mid-1970s to the mid-1980s in age groups younger than 50 years, but increased in age groups of 50 years and older.
However, since the mid-1980s, CRC incidence rates rose 2.4% annually among adults aged 20 to 29 years and 1% annually in adults aged 30 to 39 years. From the mid-1990s, rates increased 1.3% annually among adults aged 40 to 49 years and 0.5% annually among adults aged 50 to 54 years.
The rise in incidence in younger adults appeared steeper for rectal than colon cancer.
Specifically, rectal cancer rates increased 3.2% annually from 1974 to 2013 in adults aged 20 to 29 years, 3.2% annually since 1980 in adults aged 30 to 39 years, and 2.3% annually since 1990 in adults aged 40 to 49 years and 50 to 54 years. In contrast, rectal cancer rates dropped over the entire 40-year study period for adults aged 55 years and older.
In the early 1990s, half the number of adults aged 50 to 54 years had colon and rectal cancers as adults aged 55 to 59 years. In 2012 and 2013, rectal cancer incidence rates were relatively equal in the 50 to 54 years and 55 to 59 years age groups (24.7 vs. 24.5 per 100,000; IRR = 1.01, 95% CI, 0.92-1.10), and colon cancer incidence rates were only 12.4% lower in the younger group (31.9 vs. 36.4; IRR = 0.88; 95% CI, 0.81-0.94).
The proportion of diagnoses in adults aged younger than 55 years doubled from 14.6% to 29.2% for rectal cancer and increased from 11.6% to 16.6% for colon cancer.
Age-specific risk by birth cohort showed that those born in 1990 have double the risk for colon cancer (IRR = 2.4; 95% CI, 1.11-5.19) and four times the risk for rectal cancer (IRR = 4.32; 95% CI, 2.19-8.51) than those born in 1950.
In addition, in 2013, there were about 10,400 new cases of CRC diagnosed in adults aged 40 to 49 years and about 12,800 new cases in adults aged 50 to 54 years. The researchers noted those numbers are similar to the total number of cervical cancers diagnosed (12,300), for which screening is recommended for women aged 21 to 65 years.
Recommendations call for men and women to begin CRC screening at age 50 years. However, adults with a family history of CRC or a mother, father or sibling who has had a polyp, should begin screening by age 40 years, Siegel said.
“Our CRC screening guidelines [at the American Cancer Society] are currently being reviewed by an independent committee, and this study is one piece of evidence that will be included,” Siegel said. “However, screening recommendations must maximize the benefit of screening while at the same time minimizing the harms, which are rare, but include bleeding and perforation of the colon for colonoscopy screening.”
Educational campaigns are needed to alert clinicians and the general public about the rise in CRC incidence and the importance of healthier eating and more active lifestyles to try to reverse the trend, Siegel said.
“It is important to educate the public about these findings so that young people with symptoms with CRC can receive appropriate, timely follow-up in case they do have cancer,” she said. “In addition, since incidence rates are even increasing for people aged 50 to 54 years, who are already recommended to be screened, further research is necessary to understand the causes of the trend so we can stem the rising tide of premature morbidity and mortality from CRC for people in their most productive years of life.” – by Chuck Gormley
For more information:
Rebecca L. Siegel, MPH, can be reached at Surveillance and Health Services Research, American Cancer Society, 250 Williams St., NW, Atlanta, GA; email: firstname.lastname@example.org.
The American Cancer Society and NIH/NCI funded the study. The researchers report no relevant financial disclosures.