Between 2004 and 2015, the proportion of U.S. colorectal cancer (CRC) cases that were diagnosed in patients younger than age 50 years increased, a recent study found.
The retrospective study used data from the National Cancer Data Base from 2004 to 2015 to assess changes in the proportion of CRC diagnosed at an age younger than 50 years. It included 130,165 patients diagnosed at an age younger than 50 years and 1,055,598 patients diagnosed at older ages. Results were published by Cancer on July 22.
The proportion of CRC diagnoses that occurred in the under-50 population rose from 10.0% in 2004 to 12.2% in 2015 (P<0.0001). Younger patients were more likely to present with advanced disease (51.6% with stage III/IV compared to 40.0% of those ages 50 years or older). The study also found that the highest income quartile had the highest proportion of younger patients and that the proportion of younger-onset cases rose in urban areas but not rural areas.
While the causes of these findings are unclear, the study authors offered some possible explanations. The association of younger diagnosis with higher income and urban residence could indicate that lifestyle factors, such as obesity, meat consumption, and access to health care (including screening), play a role, they said. However, if the findings were due to screening, younger patients should present with earlier stages, not later, the authors noted. Another possible explanation is increased antibiotic use resulting from health care access, they said.
“Only 5.8% of cases were diagnosed at an age younger than 45 years, and this suggests that this may be an appropriate target for the screening age,” the authors said. However, they noted that the National Cancer Data Base doesn't provide data on overall disease incidence, so the results likely reflect both rising incidence in young patients and decreasing incidence in older patients. “Although the implications of these epidemiologic data support changes in screening guidelines, large prospective screening studies of patients younger than 50 years are strongly needed to determine which younger patients are most at risk for CRC and to better determine the risks, benefits, and costs of screening this population,” the authors wrote.
An accompanying editorial expressed greater reservations about changing screening recommendations based on the study's findings. “Although an increase in the incidence in any population group is a concern, the magnitude of the absolute increase is small, and colorectal cancer remains a very rare condition in younger individuals, in whom heritable risks play a larger role in comparison with older individuals,” the editorial said. Given the uncertain risk-benefit ratio of expanding screening, it is “imperative that the various hypotheses for increasing colorectal cancer incidence among people younger than 50 years be rigorously tested to determine whether changing the current screening age for people who are not at increased familial risk represents the most appropriate public health response,” the editorialist said.