The Average-Risk Age Threshold for Colorectal Cancer Screening: Should It Be Lowered?

Abstract

Screening for colorectal cancer (CRC) among average-risk adults is recommended by several guidelines organizations beginning at age 50. This age threshold was established in part because of a dramatic increase in CRC incidence during the sixth decade of life [1]. CRC screening is considered to be both effective and cost-effective in persons 50 years or older. The most recent epidemiologic data from SEER indicate that CRC incidence has continued to fall in this age group, and screening undoubtedly accounts for part of the decline. In contrast, the CRC picture for persons younger than age 50 is not as good: CRC incidence in this age group has risen. In particular, CRC incidence has increased among persons ages 40–45 from 12 per 100,000 in 1987 to 18 per 100,000 in 2006—a 50% increase over 20 years [2]. Persons younger than age 50 account for 7–9% of CRC diagnoses, tend to present with more advanced disease, and have a less favorable prognosis [3–5]. There are no published data on the effectiveness of CRC screening for persons younger than 50, and the only published model that considered this age group showed that one-time colonoscopy was not costeffective [6]. Nonetheless, other screening modalities such as fecal immunochemical testing might be useful. In light of the rising incidence and poorer prognosis of CRC in persons under age 50, should the average-risk screening age threshold be lowered to 40 years? Obtaining the answer to this complex question requires quantifying and weighing the benefits, risks, and costs of various screening modalities in persons aged 40–49 years, as compared with beginning CRC screening at age 50. Simulation models would be most appropriate for addressing this issue. One piece of information required for the models is the prevalence of clinically-important neoplasia (i.e., adenocarcinoma and advanced adenomatous polyps). What does the literature tell us about this prevalence? In this issue, Thoma and colleagues [7] report on neoplastic findings in 247 persons aged 40–49 years as compared with those of 747 persons aged 50–59. All subjects underwent first-time colonoscopy to the cecum. In addition to reporting age-related prevalence of neoplasia, the investigators report prevalence by gender, ethnicity, and body mass index (BMI). Other than the difference in age, the two groups differed in gender distribution (the proportion of women was greater in the 40–49 group) and colonoscopy indication (the proportion of screening colonoscopies was greater in the 50–59 group)—factors that would tend to have opposing effects on neoplasia prevalence. Not surprisingly, the study found that neoplasia prevalence was higher in the older age group: 22.6% versus 12.1% for any neoplasia, and 4.95% versus 2.02% for advanced adenomas. The protective effect of younger age on neoplasia prevalence persisted after adjustment for gender, race, and BMI. As in previous studies, men were more likely to have adenomas. Of some interest was the finding that higher BMI was associated with increased risk of neoplasia independent of age group, a finding that persisted in adjusted analyses. Subgroup analyses that had advanced adenoma as the outcome were not done, probably T. F. Imperiale Division of Gastroenterology and Hepatology, Department of Medicine, Indiana University School of Medicine, Indianapolis, IN, USA