Introduction. Higher body mass has been associated with elevated risk of developing colorectal cancer. However, limited prospective data are available as to whether the association differs among ethnic groups with varying degrees of susceptibility for central obesity and obesity-related metabolic diseases. We investigated potential ethnic heterogeneity in the body mass-colorectal cancer association in the Multiethnic Cohort.

Methods. Baseline self-reported data were obtained on height, weight, physical activity, diet, and other risk factors from a population-based sample of over 96,810 men and 118,441 women in Hawaii and Los Angeles who were of Caucasian, African, Japanese, Latino, and Native Hawaiian ancestry and were 45-75 years old in 1993. By December 2006, 1,575 male and 1,316 female incident colorectal cancer cases were ascertained from linkage with SEER registries. The associations of interest were estimated by multivariable-adjusted Cox proportional hazards models with age as the time metric.

Results. Prevalence of obesity at baseline (body mass index (BMI) ≥ 30) ranged from 8% in Japanese to 36% in Native Hawaiian men and from 6% in Japanese to 35-37% in African American and Native Hawaiian women. Baseline BMI was positively associated with colorectal cancer risk in men (hazard ratio (HR) for BMI ≥ 30 compared with 18.5-22.9 = 1.50 (95% confidence interval: 1.32, 1.70)) and women (HR = 1.50 (1.33, 1.70)). When examined by sex and ethnicity, men of Caucasian (HR = 1.80 (1.36, 2.39)), African (HR = 2.17 (1.48, 3.16)), and Japanese (HR = 1.80 (1.44, 2.25)) ancestry showed a positive association, whereas Latino and Native Hawaiian men showed a null association (p-interaction = 0.11). In women, the association was strongest among Native Hawaiians (HR = 2.39 (1.24, 4.60)) and Japanese Americans (HR = 2.21 (1.75, 2.79)), followed by Latinas (HR = 1.67 (1.15, 2.41)) and Caucasians (HR = 1.38 (1.07, 1.77)), while it was null among African Americans (p-interaction = 0.12).

Conclusions. These findings from a large follow-up study of diverse ethnic make-up suggest sex- and ethnicity-related heterogeneity in the body mass-colorectal cancer association, which would be important to consider for understanding the etiology and identifying higher-risk groups for intervention.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1827.