Inflammatory Bowel Disease Confers a Lower Risk of Colorectal Cancer to Females Than to Males

BACKGROUND & AIMS: Reported differences in cancer risk between male and female animals after chronic inflammation suggest that estrogen has inflammation-modifying properties. Little is known about these effects in human beings. Inflammatory bowel disease (IBD) is associated with an increased risk of colorectal cancer (CRC); we studied differences in inflammation-associated CRC between men and women patients with IBD. METHODS: By using a large population-based cohort (n = 7607) of individuals diagnosed with IBD from 1954 to 1989, we assessed the sex-specific incidence of CRC from 1960 to 2004. Incidence was determined within the cohort (modeled using Poisson regression) and compared with the general population (assessed as standardized incidence ratios) using data from national Swedish health and census registers. RESULTS: During 171,000 person-years of follow-up evaluation, 196 new cases of CRC were observed (123 in males, 73 in females). Males with IBD had a 60% higher risk of CRC (relative risk [RR], 1.6; 95% confidence interval [CI], 1.2-2.2) than females (cumulative incidence 40 years after IBD diagnosis, 8.3% vs 3.5%). Compared with the rate of CRC among the general population, in males with IBD the RR was 2.6 and the 95% CI was 2.2-3.1, whereas in females the RR was 1.9 and the 95% CI was 1.5-2.4. The effect of sex was limited to the period after 10 years of follow-up evaluation (RR, 0.8 before vs 2.2 after), and to patients diagnosed before age 45 (RR, 2.1 before vs 1.0 after). CONCLUSIONS: IBD confers a lower risk of CRC to females than to males.