Background: Cadmium is a human lung carcinogen, and recent evidence suggests it may play a role in hormone-related cancers because of its estrogenic activity. Case-control studies consistently show higher cadmium concentrations in urine from women diagnosed with breast cancer compared with control women. Our aim was to investigate the association between urinary cadmium and breast cancer in a prospective design.
Methods: We conducted a case-cohort study using the population-based Danish Diet Cancer and Health Cohort. Women age 50 to 64 years were recruited in 1993–1997 and provided urine for analysis. We identified 900 incident case patients in the Danish Cancer Registry and compared with 898 individuals in a subcohort. Urine samples collected at enrollment into the cohort were analyzed for cadmium and creatinine. We estimated incidence rate ratios (IRRs) for breast cancer in Cox proportional hazards models with age as time axis and calculated 95% confidence intervals (CIs).
Results: The linear analysis showed no association between urinary cadmium and risk for breast cancer (IRR = 1.00, 95% CI = 0.81 to 1.24 per ng Cd/mL urine). The categorical analyses showed a slightly higher risk for breast cancer for the second (IRR = 1.10, 95% CI = 0.86 to 1.42) and third (IRR = 1.14, 95% CI = 0.83 to 1.55) exposure tertiles compared with the lowest tertile. Results were similar in analyses of breast cancer subtypes defined by estrogen and progesterone receptor status and by histology, and analyses stratified by years from baseline to diagnosis.
Conclusions: This large prospective study showed no association between urinary concentration of cadmium and subsequent risk for development of postmenopausal breast cancer.
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