Women with a prior diagnosis of breast cancer are not at an increased risk for subsequent colorectal cancer

BACKGROUND: Earlier studies regarding the risk of colorectal cancer in women with a prior diagnosis of breast cancer yielded conflicting results. METHODS: 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. RESULTS: 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. CONCLUSION: Women with a prior diagnosis of breast cancer are not at an increased risk of colorectal cancer; these women can follow average risk screening guidelines for colorectal cancer.