Abstract 281: Site specific risk factors for colorectal cancer
Authors: Gupta Samir , Bustamante Ranier , Earles Ashley , Martinez Maria E. , Messer Karen , Williams Christina D. , Gawron Andrew J. , Kaltenbach Tonya , Liu Lin 
Published: July 2017

Abstract
Background: Most studies of colorectal cancer (CRC) risk factors pool cases across anatomical sites, though tumor characteristics and embryologic origins differ. Our aim was to conduct a site-stratified (proximal, distal, rectal) case control study of candidate risk factors for CRC.
Methods: Our study base was US Veterans with &gt;1 colonoscopy 1999-2011. CRC cases at baseline colonoscopy were identified with the Veterans Affairs Central Cancer Registry. Controls had normal colonoscopy without biopsy, no history of CRC, and no CRC within 3 years of index colonoscopy. Age, sex, race/ethnicity, body mass index (BMI), diabetes, and smoking were considered candidate risk factors. Primary outcome was CRC, stratified by site. Site-specific odds ratios (OR) and 95% confidence intervals (CI) for each risk factor were computed with unadjusted and adjusted multinomial logistic regression models.
Results: We identified 21,739 CRC cases and 616,323 normal colonoscopy controls. For cases combined vs. controls, median age was 68 vs. 61 years, 98% vs. 95% were male, median BMI was 27.8 vs. 28.8 kg/m2, 28% vs. 24% had diabetes, and 25% vs. 29% were non-smokers; race/ethnicity was similar. Presence and strength of associations differed by risk factor and CRC site (Table). Smoking was more closely associated with rectal (OR=1.84) than proximal (OR=1.59) or distal cancer (OR=1.50). Diabetes was more closely associated with proximal than distal or rectal cancer (OR=1.28, 1.17 and 1.12, respectively). Blacks had reduced odds for rectal (OR=0.89), but increased odds for distal (OR=1.27) and particularly proximal cancer (OR=1.60) when compared to non-Hispanic whites. For males vs. females, odds of rectal was higher than distal or proximal cancer (OR=2.64, 1.95 and 1.32, respectively).
Conclusions: Presence and strength of association of cancer risk factors may differ by CRC site. Site should be a key consideration in future studies of CRC risk.
Table 1.Site specific risk factors for 21,739 CRC cases compared to 616,323 normal colonoscopy controlsAnatomic Site of CRC*Proximal (n=7,686)Distal (n=7,036)Rectal (n=7,017)Candidate Risk FactorOR (CI)OR (CI)OR (CI)Age, years†1.100 (1.096-1.103)1.065 (1.062-1.069)‡1.055 (1.051- 1.059)‡§Gender, male vs. female1.318 (1.080-1.608)1.950 (1.538-2.471)‡2.636 (2.006-3.463)‡Race/ethnicityBlack vs. non-Hispanic white1.596 (1.480-1.720)1.270 (1.167-1.381)‡0.886 (0.808-0.971)‡§Hispanic vs. non-Hispanic white1.291 (1.123-1.485)1.531 (1.337-1.753)1.219 (1.053-1.411)§Asian vs. non-Hispanic white0.872 (0.634-1.201)0.917 (0.662-1.272)0.556 (0.371-0.832)BMI, kg/m2†0.994 (0.988-1.000)1.005 (0.999-1.012)‡0.963 (0.957-0.970)‡§Diabetes, yes vs. no1.278 (1.196-1.366)1.170 (1.089-1.257)1.119 (1.038-1.207)‡SmokingCurrent vs. never1.594 (1.476-1.722)1.500 (1.383-1.627)1.837 (1.695-1.992)‡§Former vs. never0.997 (0.926-1.073)1.082 (1.001-1.171)1.085 (0.998-1.119)* Multinomial analyses adjusted for other risk factors, as well as year of colonoscopy, 1999-2011† by one unit increment‡ p&lt;0.05 when compared to proximal cancer§ p&lt;0.05 when compared to distal cancerCRC, colorectal cancer; BMI, body mass index.
Citation Format: Samir Gupta, Ranier Bustamante, Ashley Earles, Maria E. Martinez, Karen Messer, Christina D. Williams, Andrew J. Gawron, Tonya Kaltenbach, Lin Liu. Site specific risk factors for colorectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 281. doi:10.1158/1538-7445.AM2017-281