Objective: To investigate risk factors for colorectal cancer following breast cancer.
Methods: In this nested case-control study, all women (n = 14,900) with a first primary breast cancer (1978-1992) were identified from the western Washington population-based Surveillance, Epidemiology, and End Results Cancer Registry. Cases (n = 160) developed a second primary colorectal cancer before 1995, at least 6 months after the first cancer diagnosis. Controls (n = 310, matched to the cases on calendar year, age and breast cancer stage) were randomly selected from those who did not develop a second primary cancer and who survived to the case's colorectal cancer diagnosis date. Characteristics of the cases and controls at initial diagnosis were compared using conditional logistic regression.
Results: The incidence of colorectal cancer was associated with a family history of breast cancer (v.s. no family history, matched odds ratio (mOR) = 2.1, 95% confidence interval (CI): 1.1-4.1), high body mass index (> or = 30kg/m2 v.s. < 30kg/m2, mOR = 2.2, CI: 1.2-3.9), and lobular breast cancer histology (v.s. ductal, mOR = 2.0, CI: 0.9-4.4). Risk was unrelated to menopausal status, prior hormone replacement therapy and estrogen/progesterone receptor status of the breast tumors.
Conclusions: The risk of developing a second primary colorectal cancer may be elevated among certain subsets of breast cancer patients.