Background: Summaries of colorectal cancer risk factors often mention breast cancer history – but data on breast cancer history as a colorectal cancer risk factor are equivocal. Objective: Compare colorectal cancer incidence in a large cohort of women diagnosed with breast cancer (overall risk and risk for subgroups defined by ethnicity and age and stage at diagnosis) to that of the general population. Methods: We conducted a retrospective cohort analysis using 1974-1995 Surveillance, Epidemiology and End Results (SEER) data. Colon and rectal cancer incidence in the SEER breast cancer cohort was compared to general female population incidence using standardized incidence ratios (SIRs) adjusting for age, race, and calendar time. Stratified SIRs and SIRs from poisson regressions adjusting simultaneously for all study variables were also estimated. Results: 227,165 women with breast cancer, from which there were 2,862 subsequent incident colorectal cancers cases, were identified. Colon and rectal cancer incidence in the breast cancer cohort was lower than in the general population (SIR 0.95 95% CI, 0.91-0.99 and SIR 0.87 95% CI, 0.81-0.94, respectively). The smallest SIRs (largest relative rate decreases) were seen in white women, older women, and in the initial six months following breast cancer diagnosis. Conclusions: These data provide no evidence that breast cancer is associated with increased colon or rectal cancer risk. Reduced risks observed could be attributable to behavior change (risk factor modification and/or increased screening for precancerous colorectal lesions) secondary to breast cancer diagnosis or to breast cancer risk factor(s) that also protect against colorectal cancer.
Learning Objectives: 1) Become familiar with current thinking on the association between a history of breast cancer and risk of subsequent colorectal cancer 2) Understand what the most recent SEER data indicate about colorectal cancer risk following breast cancer diagnosis
Keywords: Breast Cancer, Cancer
Presenting author's disclosure statement:
Organization/institution whose products or services will be discussed: None
I do not have any significant financial interest/arrangement or affiliation with any organization/institution whose products or services are being discussed in this session.