Colorectal Cancer Risk Influenced by Sex, Age, and Birth Year

Roxanne Nelson

June 02, 2010

June 2, 2010 — Men have a higher prevalence of colorectal cancer and advanced disease, according to an analysis of data from a national German colonoscopy screening program. The prevalence of colorectal cancer and advanced neoplasm moderately increased with age, but was higher in men than in women in all age groups.

The researchers, reporting in the June 1 issue of the Annals of Internal Medicine, also looked at the age-specific prevalence of advanced colorectal neoplasms by birth cohort among men and women. They observed a strong cohort effect that showed increases in prevalence in later birth cohorts, as opposed to earlier, birth cohorts.

This strong cohort effect, note the authors, "is disquieting because it might indicate an increasing burden of colorectal neoplasm in the years to come."

Prevalence Higher in Men

Previous studies have shown that the risk for colorectal cancer increases with age, and that the risk is higher in men than in women. However, previous research has not separated the influence of age from the influence of birth cohort (year of birth). In the current study, Hermann Brenner, MD, MPH, from the German Cancer Research in Heidelberg, and colleagues sought to estimate the effects of age and birth cohort in advanced colorectal cancer among people who participated in the German colonoscopy screening program.

Another goal of the study was to adjust risk-advancement periods for men, compared with women, for birth cohort effects.

The study population consisted of 2,185,153 people 55 to 75 years of age who participated in a colon cancer screening program in Germany from 2005 to 2007. The majority of participants were women, particularly in the younger age groups.

A total of 17,196 participants (0.8%) had colorectal cancer, and 152,429 (7.0%) had any type of advanced cancer. Overall, the prevalence of colorectal cancer and advanced neoplasm showed a moderate increase with age and in all age groups was higher in men than in women.

In each age group, prevalence was up to 2 times higher in men than in women. The prevalence of colorectal cancer in men 55, 60, and 65 years of age was reached in much older women — 63, 69, and 74 years, respectively. The authors observed that the prevalence of any advanced neoplasm in men 55 years of age was reached in women at 70 years. Likewise, prevalence in men at 60 and 65 years was not attained by women who were 75 years of age.

Colonoscopy Findings by Age and Sex

Age, y Number of Participants Colorectal Cancer, n (%) Any Advanced Cancer, n (%)
Men      
55–59 236,028 1,422 (0.6) 16,810 (7.1)
60–64 272,832 2,494 (0.9) 24,255 (8.9)
65–69 281,400 3,388 (1.2) 28,491 (10.1)
70–75 170,073 3,056 (1.8) 19,646 (11.6)
All men 960,333 10,360 (1.1) 89,202 (9.3)
Women      
55–59 351,716 1,090 (0.3) 13,351 (3.8)
60–64 354,559 1,633 (0.5) 17,352 (4.9)
65–69 330,965 2,183 (0.7) 19,224 (5.8)
70–75 187,580 1,930 (1.0) 13,300 (7.1)
All women 1,224,820 6,836 (0.6) 63,227 (5.2)


Controlling for Birth Cohort

In a cross-sectional analysis, the researchers found that the prevalence of colorectal cancer increased modestly — a 2.1-fold increase per decade of age. However, after controlling for birth cohort or year, the age gradient increased to almost 6-fold per decade of age.

For any advanced neoplasm, the authors note that the age gradient was less pronounced. As for colorectal cancer, the age gradient was much stronger after controlling for birth cohort than in the cross-sectional analysis (relative prevalence, 2.3 vs 1.4). The prevalence for advanced disease increased 1.6-fold per decade of birth year.

Again in the cross-sectional analysis, the risk-advancement periods for men vs women were estimated to be 8.4 years for colorectal cancer and 16.1 years for any advanced tumor. After controlling for birth cohort, these numbers were less pronounced but still substantial (3.4 and 6.9 years, respectively).

They also compared risk-advancement periods for later and earlier birth cohorts, which were 5.9 years for colorectal cancer and 5.7 years for any advanced cancer per decade of birth.

Reasons Remain Unclear

Although the authors were unable to determine the reason for the strong cohort effect, they speculated that it could be the result of a number of factors, including unfavorable shifts in risk-factor distributions such as obesity, diabetes, and smoking among women.

They also note that, in theory, the cohort effect could "reflect the changes in the composition of the screening population over time — that is, greater use of screening colonoscopy by those with prevalent neoplasms in later years, or enhanced detection of advanced colorectal neoplasms by endoscopists in later years."

The authors conclude that "risk-advancement periods of substantial length persist, and their potential relevance for screening policies requires careful further evaluation." As far as the increasing prevalence of colorectal neoplasms in later birth cohorts, efforts are needed to identify, stabilize, and ideally reverse unfavorable risk-factor trends should be a priority for prevention.

This study did not have outside funding sources. The researchers have disclosed no relevant financial relationships.

Ann Intern Med. 2010;152:697-703. Abstract

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