Despite the substantial morbidity associated with colorectal cancer and the widespread adoption of screening recommendations that apply to asymptomatic average-risk persons at age 50, the prevalence of preneoplastic colorectal adenomas in the preceding decade has had little study. The sole previous analysis of the prevalence of adenomas in this age group in the United States found an adenoma prevalence of 11%, with a prevalence of advanced adenomas of 3.5%, rates similar to our findings ().(9
) Similar findings in this age group were reported among average risk men in South Korea, though in that study the prevalence of adenomas and advanced neoplasia among women was significantly lower.(10
Prevalence of adenomas, advanced neoplasms, and colorectal cancer among patient groups aged 40-49 and 50-59.
Prior studies of asymptomatic patients older than 50 years found a prevalence of adenoma and advanced neoplasia that was considerably higher than those in our cohort. For example, in one large cohort, the prevalence of colorectal neoplasia was 37.5%.(4
) However, more than two thirds of this cohort consisted of subjects between 60 and 75 years. Moreover, 13.9% of individuals in that population had one or more first degree relatives with a history of colorectal cancer. Other cohorts demonstrating a similarly high prevalence of adenomas among asymptomatic patients older than 50 years had a large proportion of patients older than 59 and included those with a family history of colorectal cancer.(11
) Our study excluded such patients so as to compare the prevalence of colorectal neoplasia in two age deciles in an average-risk population. This most likely accounts for the relatively lower prevalence of adenomas in our cohort as compared to prior studies.
We did not find a significant difference in the overall prevalence of adenomas between the 40-49 age group and the 50-59 age group. However, we did observe an increase in the prevalence of advanced neoplasms in the 50-59 age group compared to the 40-49 age group. Although this near-doubling of the prevalence of advanced neoplasms was not statistically significant, we suspect that there is a true rise in the prevalence of advanced neoplasms between these two decades that our study was not adequately powered to observe. Post-hoc power analyses show that the smallest difference in the prevalence of advanced tumors that could be observed with 80% power was 2% in the 40-49 year old group versus 6% in the 50-59 year old group. This rise was noted as well in the study by Imperiale, et al, in which the rise in prevalence of advanced neoplasms continued in subsequent decades of life. (9
) A rise in the prevalence of advanced neoplasms in the 50-59 age group as compared to the 40-49 age group would account for the well-established subsequent parallel rise in the prevalence of colorectal cancer in later decades.
An actuarial analysis of colonoscopy for colorectal cancer screening is required to determine whether screening the asymptomatic population beginning at age 40 would prevent enough morbidity and mortality to be cost effective; such cost efficacy analyses have been performed on colonoscopy as a screening modality, but have generally considered age 50 to be the age of initiation of screening,(13
) with only one such analysis considering one-time screening at age 45-49.(15
A recent study by Regula, et al, analyzing the results of a national screening program in Poland, found that the prevalence of advanced colorectal neoplasia in men age 40-49 was similar to that of women age 50-59, suggesting that the age at which to commence screening should be gender-specific.(16
) However, individuals in the 40-49 age bracket in that study were eligible for screening only if there were a family history of cancer of any kind; this does not represent the average risk population, even when limiting the analysis to those with a family history of malignancy other than colorectal cancer. Nonetheless, our results are similar in that, among men the prevalence of adenoma was the same in the two age groups, and was slightly higher among 50-59 year old women than among 40-49 year old women.
Our study has a number of limitations. As noted above, the population is predominantly male and Caucasian, limiting the ability to evaluate gender and race as a risk factor for colorectal neoplasia due to a relative lack of comparators. Dietary and medication data, which may affect development of adenomas, were not collected; nevertheless, one would not expect there to be a large difference in diet or medication use between the two age brackets that would have a substantial impact on our findings. As this was an observational study, the decision of the patient to proceed with colonoscopy during age 40-49 years may have been due to factors associated with an increased risk of adenoma or carcinoma, such as rectal bleeding. We excluded from our analysis those patients who were noted to have an indication for colonoscopy other than screening, but the possibility remains that some of the patients in the 40-49 bracket were of above-average risk for colorectal neoplasia. Furthermore, our study focused on an employed population provided with wellness exams by their employers. Thus, the results may not be generalizable to other groups.
Our analysis demonstrates that there is little difference in the overall prevalence of colorectal adenomas when we compared asymptomatic individuals age 40-49 to those age 50-59 years. Despite the similar adenoma prevalence between the two age groups, we detected an increased prevalence of advanced neoplasia in the 50-59 age group that was not statistically significant, possibly due to sample size limitations. We suspect that future sufficiently powered studies will demonstrate a true rise in the prevalence of advanced neoplasia when comparing these two age groups. Future studies are also required to determine the cost-efficacy of screening with colonoscopy at age 40, and to develop non-invasive methods to further risk-stratify those whom we currently consider to be at average risk for colorectal cancer.