['Earlier studies regarding the risk of colorectal cancer in women with a prior diagnosis of breast cancer yielded conflicting results.', 'A retrospective cohort study was performed using the General Practitioner Research Database of the United Kingdom. Women with a prior diagnosis of breast cancer were compared with female control patients without a prior history of breast cancer. The primary outcome was an incident diagnosis of colorectal cancer. Poisson regression analysis was utilized to assess the effects of potential confounder variables.', 'The study included 17,415 breast cancer patients and 69,660 matched control patients with follow-up time in person years of 52,914 and 331,480, respectively. The relative rate of colorectal cancer among breast cancer patients was 0.80 (95% CI 0.56-1.15). The relative rate of colorectal cancer among women exposed and unexposed to tamoxifen were 0.73 (95% CI 0.49-1.08) and 1.81 (95% CI 0.85-3.85), respectively.'] Are women with a prior diagnosis of breast cancer at an increased risk for subsequent colorectal cancer?