Abstract 2166: A prospective study on oral contraceptive use and risk of colorectal adenomas
Authors: Charlton Brittany M. , Giovannucci Ed , Fuchs Charles S. , Missmer Stacey A. , Rosner Bernard A. , Wu Kana , Michels Karin B. 
Published: May 2015

Abstract
Background: Most colorectal cancers (CRC) arise from colorectal adenomas. The influence of reproductive factors on CRC, including oral contraceptive (OC) use, has been examined for a number of years, but less research is available on the role of OC use on adenomas. A better understanding of this association will provide insight into the mechanism through which hormones impact colorectal carcinogenesis.
Objective: To examine the association of OC use and colorectal adenomas using detailed data from a large prospective cohort study with 32 yrs of follow-up data.
Design: The Nurses' Health Study was established in 1976 when 121,701 female registered nurses 30-55 yrs of age completed a mailed questionnaire on medical history and lifestyle factors. We assessed OC use every 2 yrs between 1976-1982 and categorized this use according to ever (≥2 mo) and never use (reference), duration of use (never, ≤1, &gt;1-&lt;2, ≥2-&lt;5, ≥5-&lt;10, 10+ yrs), and time since last use (never, ≤4, &gt;4-&lt;10, ≥10-&lt;15, 15+ yrs). Participants had to undergo a lower bowel endoscopy during the study period to be eligible for the current analyses. All colorectal adenoma cases identified at endoscopy were included from 1986 (when endoscopies were first accessed) through 2010; cases were stratified by subsite (proximal, distal, rectal), stage/size (small/early, large/advanced), and number of adenomas (1, 2+).
Methods: Multivariable logistic regression models for clustered data were used to estimate odds ratios [OR (95% CIs)]. Models were adjusted for age, body mass index, height, physical activity, smoking, processed and red meat, folate, calcium, total energy, alcohol, aspirin use, age at first birth, parity, hormone therapy use/duration, family history of CRC, time period, as well as endoscopy information including reason, number, and yr since most recent.
Results: Among 70,164 participants who had a lower bowel endoscopy, 49% (N=34,329) reported never using OCs and 51% (N=35,835) reported ≥2 mo of use. We recorded 2,950 never-users with an adenoma compared to 3,075 ever-users. Ever OC use was associated with a slight increase of small/early stage adenomas [OR=1.12 95% CI (1.03-1.22)] but not with large/advanced stage adenomas or any other category (e.g., number of adenomas). Duration of OC use was not associated with adenomas but longer times since last OC use were associated with increased odds for all of the adenoma outcomes [e.g., compared to never use, 15+ yrs since last use for all adenomas: OR=1.18 (1.08, 1.29)]. Shorter times since last OC use were inversely associated [e.g., ≤4 yrs since last use for all adenomas: OR=0.76 (0.67, 0.86)].
Conclusions: The null association between OC use and colorectal adenomas may be more nuanced than initially described in the literature. We found that OC use was associated with certain stages/sizes of colorectal adenomas (e.g., small/early) and further exploration of the time since last OC use associations are warranted. Support: P01CA87969, T32CA09001, T32HD060454
Citation Format: Brittany M. Charlton, Ed Giovannucci, Charles S. Fuchs, Stacey A. Missmer, Bernard A. Rosner, Kana Wu, Karin B. Michels. A prospective study on oral contraceptive use and risk of colorectal adenomas. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2166. doi:10.1158/1538-7445.AM2014-2166