Abstract LB-381: Childhood body size and the risk of colon or rectal cancer in adulthood

Background: Adult obesity and height are well-established risk factors for colorectal cancer, however, few studies have examined the possible association with childhood body size. It is therefore unknown if the association is due to the body size in adult life or may be influenced by body size already from childhood. In the present study, we examined if childhood body mass index (BMI: kg/m 2 ) and height from ages 7 to 13 years are associated with the risk of colon and rectal cancer in adulthood. Methods: We used the Copenhagen School Health Records Register to identify children who were born from 1930-1972 and had information on height and weight from their school health examinations. BMI and height were transformed into z-scores. Cases were identified by linkage to the Danish Cancer Registry using ICD-10 codes (colon: C18.0-18.9, rectal: C19.9, 20.9). Analyses were conducted using Cox proportional hazard regressions stratified by birth cohort and sex since no significant sex interactions were observed. Results: Among 257,623 individuals (49.7% women), 2,676 were diagnosed with colon cancer (47.5% women) and 1,681 with rectal cancer (38.9% women). Per z-score increase in BMI at age 13 years the hazard ratio (HR) for colon cancer in adulthood was 1.09 (95% confidence interval [CI]: 1.04 to 1.14) in sex-stratified analyses. Per z-score increase in height at age 13 years the HR for colon cancer in adulthood was 1.14 (95% CI: 1.09 to 1.19). In a model including BMI and height (thus comparing two children of the same height with different weights and vice versa), the effect of BMI was attenuated (HR per z-score of BMI: 1.05, 95% CI: 1.00 to 1.10) but the HR for height changed little (HR per z-score of height: 1.13, 95% CI: 1.08 to 1.17). Essentially similar results were observed at all other ages (7 to 12 years). Examining the associations by colon sub-sites showed that the results observed mainly were driven by the associations with sigmoid colon cancer (C18.7, 1100 cases). Per z-score unit increase in BMI at age 13 years the HR was 1.11 (95% CI: 1.04 to 1.19) for a cancer in sigmoid colon as adult, while the HR for height was 1.21 (95% CI: 1.14 to 1.29). Associations between BMI and rectal cancer were generally not significant, at age 13 years the HR was 0.97 (95% CI: 0.92 to 1.03). Overall similar results were observed at ages 7-10 years and at age 12 years. Only at age 11 years was a borderline significant association observed, with a HR of 0.95 (95% CI: 0.89 to 1.00) per unit of BMI z-score. For height no significant associations were observed with the later risk of rectal cancer, at age 13 years the HR was 1.03 (95% CI: 0.98 to 1.08) and essentially similar results were observed at ages 7 to 12 years. Conclusion: Body size in childhood was positively associated with the later risk of colon cancer, whereas no associations were observed for rectal cancer. However, the results indicate that among children the associations observed between body size and colon cancer were mainly but not exclusively explained by height. Citation Format: Britt W. Jensen, Michael Gamborg, Ismail Gogenur, Thorkild I.A. Sorensen, Jennifer L. Baker. Childhood body size and the risk of colon or rectal cancer in adulthood. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr LB-381.